[dart2js] Add dart:_dart2js_runtime_metrics library and package

The internal dart:_dart2js_runtime_metrics library is accessed via
package:dart2js_runtime_metrics.

There is currently one API: startupMetrics.

On non-dart2js configurations the API is stubbed for ease-of-use.

Change-Id: I80c56a83fd166ec19c3846fb6937cf0440ed2c6b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/208563
Commit-Queue: Stephen Adams <sra@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>

.dart_tool/package_config.json

@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2021-07-27T19:27:52.638315",
+  "generated": "2021-07-30T20:37:49.663747",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -204,6 +204,12 @@
       "packageUri": "lib/",
       "languageVersion": "2.3"
     },
+    {
+      "name": "dart2js_runtime_metrics",
+      "rootUri": "../pkg/dart2js_runtime_metrics",
+      "packageUri": "lib/",
+      "languageVersion": "2.14"
+    },
     {
       "name": "dart2js_tools",
       "rootUri": "../pkg/dart2js_tools",

.packages

@@ -30,6 +30,7 @@ convert:third_party/pkg/convert/lib
 crypto:third_party/pkg/crypto/lib
 csslib:third_party/pkg/csslib/lib
 dart2js_info:third_party/pkg/dart2js_info/lib
+dart2js_runtime_metrics:pkg/dart2js_runtime_metrics/lib
 dart2js_tools:pkg/dart2js_tools/lib
 dart2native:pkg/dart2native/lib
 dart_internal:pkg/dart_internal/lib

pkg/compiler/lib/src/common_elements.dart

@@ -388,6 +388,9 @@ abstract class CommonElements {
   /// Holds the method "requiresPreamble" in _js_helper.
   FunctionEntity get requiresPreambleMarker;
 
+  /// Holds the method "_rawStartupMetrics" in _js_helper.
+  FunctionEntity get rawStartupMetrics;
+
   FunctionEntity get loadLibraryWrapper;
 
   FunctionEntity get loadDeferredLibrary;
@@ -1665,6 +1668,11 @@ class CommonElementsImpl
   FunctionEntity get requiresPreambleMarker =>
       _requiresPreambleMarker ??= _findHelperFunction('requiresPreamble');
 
+  FunctionEntity _rawStartupMetrics;
+  @override
+  FunctionEntity get rawStartupMetrics =>
+      _rawStartupMetrics ??= _findHelperFunction('rawStartupMetrics');
+
   @override
   FunctionEntity get loadLibraryWrapper =>
       _findHelperFunction("_loadLibraryWrapper");

pkg/compiler/lib/src/js_backend/backend_usage.dart

@@ -51,6 +51,9 @@ abstract class BackendUsage {
   /// `true` if 'dart:mirrors' features are used.
   bool get isMirrorsUsed;
 
+  /// `true` if startup timestamps are used.
+  bool get requiresStartupMetrics;
+
   /// `true` if `noSuchMethod` is used.
   bool get isNoSuchMethodUsed;
 
@@ -120,6 +123,9 @@ class BackendUsageBuilderImpl implements BackendUsageBuilder {
   /// `true` if a core-library function requires the preamble file to function.
   bool requiresPreamble = false;
 
+  /// `true` if a core-library function accesses startup timestamps.
+  bool requiresStartupMetrics = false;
+
   @override
   bool isFunctionApplyUsed = false;
 
@@ -242,6 +248,8 @@ class BackendUsageBuilderImpl implements BackendUsageBuilder {
       isFunctionApplyUsed = true;
     } else if (member.library == _commonElements.mirrorsLibrary) {
       isMirrorsUsed = true;
+    } else if (member == _commonElements.rawStartupMetrics) {
+      requiresStartupMetrics = true;
     }
   }
 
@@ -275,7 +283,7 @@ class BackendUsageBuilderImpl implements BackendUsageBuilder {
 
   @override
   BackendUsage close() {
-    return new BackendUsageImpl(
+    return BackendUsageImpl(
         globalFunctionDependencies: _globalFunctionDependencies,
         globalClassDependencies: _globalClassDependencies,
         helperFunctionsUsed: _helperFunctionsUsed,
@@ -283,6 +291,7 @@ class BackendUsageBuilderImpl implements BackendUsageBuilder {
         needToInitializeIsolateAffinityTag: _needToInitializeIsolateAffinityTag,
         needToInitializeDispatchProperty: _needToInitializeDispatchProperty,
         requiresPreamble: requiresPreamble,
+        requiresStartupMetrics: requiresStartupMetrics,
         runtimeTypeUses: _runtimeTypeUses,
         isFunctionApplyUsed: isFunctionApplyUsed,
         isMirrorsUsed: isMirrorsUsed,
@@ -316,6 +325,9 @@ class BackendUsageImpl implements BackendUsage {
   @override
   final bool requiresPreamble;
 
+  @override
+  final bool requiresStartupMetrics;
+
   @override
   final bool isFunctionApplyUsed;
 
@@ -336,6 +348,7 @@ class BackendUsageImpl implements BackendUsage {
       this.needToInitializeIsolateAffinityTag,
       this.needToInitializeDispatchProperty,
       this.requiresPreamble,
+      this.requiresStartupMetrics,
       Set<RuntimeTypeUse> runtimeTypeUses,
       this.isFunctionApplyUsed,
       this.isMirrorsUsed,
@@ -364,12 +377,13 @@ class BackendUsageImpl implements BackendUsage {
     bool needToInitializeIsolateAffinityTag = source.readBool();
     bool needToInitializeDispatchProperty = source.readBool();
     bool requiresPreamble = source.readBool();
+    bool requiresStartupMetrics = source.readBool();
     bool isFunctionApplyUsed = source.readBool();
     bool isMirrorsUsed = source.readBool();
     bool isNoSuchMethodUsed = source.readBool();
     bool isHtmlLoaded = source.readBool();
     source.end(tag);
-    return new BackendUsageImpl(
+    return BackendUsageImpl(
         globalFunctionDependencies: globalFunctionDependencies,
         globalClassDependencies: globalClassDependencies,
         helperFunctionsUsed: helperFunctionsUsed,
@@ -378,6 +392,7 @@ class BackendUsageImpl implements BackendUsage {
         needToInitializeIsolateAffinityTag: needToInitializeIsolateAffinityTag,
         needToInitializeDispatchProperty: needToInitializeDispatchProperty,
         requiresPreamble: requiresPreamble,
+        requiresStartupMetrics: requiresStartupMetrics,
         isFunctionApplyUsed: isFunctionApplyUsed,
         isMirrorsUsed: isMirrorsUsed,
         isNoSuchMethodUsed: isNoSuchMethodUsed,
@@ -399,6 +414,7 @@ class BackendUsageImpl implements BackendUsage {
     sink.writeBool(needToInitializeIsolateAffinityTag);
     sink.writeBool(needToInitializeDispatchProperty);
     sink.writeBool(requiresPreamble);
+    sink.writeBool(requiresStartupMetrics);
     sink.writeBool(isFunctionApplyUsed);
     sink.writeBool(isMirrorsUsed);
     sink.writeBool(isNoSuchMethodUsed);

pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart

@@ -14,8 +14,8 @@ import '../common_elements.dart';
 import 'code_emitter_task.dart' show Emitter;
 
 class MainCallStubGenerator {
-  static jsAst.Statement generateInvokeMain(
-      CommonElements commonElements, Emitter emitter, FunctionEntity main) {
+  static jsAst.Statement generateInvokeMain(CommonElements commonElements,
+      Emitter emitter, FunctionEntity main, bool requiresStartupMetrics) {
     jsAst.Expression mainAccess = emitter.staticFunctionAccess(main);
     jsAst.Expression currentScriptAccess =
         emitter.generateEmbeddedGlobalAccess(embeddedNames.CURRENT_SCRIPT);
@@ -90,6 +90,10 @@ class MainCallStubGenerator {
         }
       })(function(currentScript) {
         #currentScript = currentScript;
+
+        if (#startupMetrics) {
+          init.#startupMetricsEmbeddedGlobal.add('callMainMs');
+        }
         var callMain = #mainCallClosure;
         if (typeof dartMainRunner === "function") {
           dartMainRunner(callMain, []);
@@ -98,7 +102,9 @@ class MainCallStubGenerator {
         }
       })''', {
       'currentScript': currentScriptAccess,
-      'mainCallClosure': mainCallClosure
+      'mainCallClosure': mainCallClosure,
+      'startupMetrics': requiresStartupMetrics,
+      'startupMetricsEmbeddedGlobal': embeddedNames.STARTUP_METRICS,
     });
   }
 }

pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart

@@ -294,8 +294,8 @@ class ProgramBuilder {
   }
 
   js.Statement _buildInvokeMain() {
-    return MainCallStubGenerator.generateInvokeMain(
-        _commonElements, _task.emitter, _mainFunction);
+    return MainCallStubGenerator.generateInvokeMain(_commonElements,
+        _task.emitter, _mainFunction, _backendUsage.requiresStartupMetrics);
   }
 
   DeferredFragment _buildDeferredFragment(LibrariesMap librariesMap) {

pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart

@@ -35,6 +35,15 @@ part of dart2js.js_emitter.startup_emitter.model_emitter;
 // reducing their size.
 const String _mainBoilerplate = '''
 (function dartProgram() {
+
+if (#startupMetrics) {
+  // Stash the metrics on the main unit IIFE.
+  // TODO(sra): When the JavaScript local renamer is more intelligent, we can
+  // simply use a local variable.
+  (dartProgram.$STARTUP_METRICS = ${ModelEmitter.startupMetricsGlobal})
+      .add("dartProgramMs");
+}
+
 // Copies the own properties from [from] to [to].
 function copyProperties(from, to) {
   var keys = Object.keys(from);
@@ -469,7 +478,7 @@ convertToFastObject(#staticState);
 
 // Invokes main (making sure that it records the 'current-script' value).
 #invokeMain;
-})()
+})();
 ''';
 
 /// An expression that returns `true` if `__proto__` can be assigned to stitch
@@ -720,6 +729,7 @@ class FragmentEmitter {
       'staticStateDeclaration': DeferredHolderParameter(),
       'staticState': DeferredHolderParameter(),
       'holders': holderDeclaration,
+      'startupMetrics': _closedWorld.backendUsage.requiresStartupMetrics,
 
       // Tearoff parameters:
       'tpContainer': js.string(TearOffParametersPropertyNames.container),
@@ -1847,6 +1857,12 @@ class FragmentEmitter {
                 r'    : "$ti"')
             : js.js(r'Symbol("$ti")')));
 
+    if (_closedWorld.backendUsage.requiresStartupMetrics) {
+      // Copy the metrics object that was stored on the main unit IIFE.
+      globals.add(js.Property(
+          js.string(STARTUP_METRICS), js.js('dartProgram.$STARTUP_METRICS')));
+    }
+
     js.ObjectInitializer globalsObject =
         js.ObjectInitializer(globals, isOneLiner: false);
 

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

@@ -25,6 +25,7 @@ import 'package:js_runtime/shared/embedded_names.dart'
         NATIVE_SUPERCLASS_TAG_NAME,
         RTI_UNIVERSE,
         RtiUniverseFieldNames,
+        STARTUP_METRICS,
         TearOffParametersPropertyNames,
         TYPE_TO_INTERCEPTOR_MAP,
         TYPES;
@@ -136,6 +137,8 @@ class ModelEmitter {
   static const String deferredInitializersGlobal =
       r"$__dart_deferred_initializers__";
 
+  static const String startupMetricsGlobal = r'$__dart_startupMetrics';
+
   static const String partExtension = "part";
   static const String deferredExtension = "part.js";
 
@@ -372,6 +375,32 @@ class ModelEmitter {
         {'deferredInitializers': deferredInitializersGlobal});
   }
 
+  js.Statement buildStartupMetrics() {
+    // We want the code that initializes the startup metrics to execute as early
+    // as possible, so it is placed ahead of the main program IIFE instead of,
+    // e.g. as a parameter of the IIFE. It is OK to use a top-level variable,
+    // since the IIFE immediately reads the variable.
+    return js.js.statement('''
+var ${startupMetricsGlobal} =
+(function(){
+  // The timestamp metrics use `performance.now()`. We feature-detect and
+  // fall back on `Date.now()` for JavaScript run in a non-browser evironment.
+  var _performance =
+      (typeof performance == "object" &&
+       performance != null &&
+       typeof performance.now == "function")
+          ? performance
+          : Date;
+  var metrics = {
+    a: [],
+    now: function() { return _performance.now() },
+    add: function(name) { this.a.push(name, this.now()); }
+  };
+  metrics.add('firstMs');
+  return metrics;
+})();''');
+  }
+
   // Writes the given [fragment]'s [code] into a file.
   //
   // Updates the shared [outputBuffers] field with the output.
@@ -395,6 +424,8 @@ class ModelEmitter {
       buildGeneratedBy(),
       js.Comment(HOOKS_API_USAGE),
       if (isSplit) buildDeferredInitializerGlobal(),
+      if (_closedWorld.backendUsage.requiresStartupMetrics)
+        buildStartupMetrics(),
       code
     ]);
 

pkg/compiler/lib/src/js_model/js_world_builder.dart

@@ -256,7 +256,7 @@ class JsClosedWorldBuilder {
           map.toBackendType(runtimeTypeUse.argumentType));
     }).toSet();
 
-    return new BackendUsageImpl(
+    return BackendUsageImpl(
         globalFunctionDependencies: globalFunctionDependencies,
         globalClassDependencies: globalClassDependencies,
         helperFunctionsUsed: helperFunctionsUsed,
@@ -266,6 +266,7 @@ class JsClosedWorldBuilder {
         needToInitializeDispatchProperty:
             backendUsage.needToInitializeDispatchProperty,
         requiresPreamble: backendUsage.requiresPreamble,
+        requiresStartupMetrics: backendUsage.requiresStartupMetrics,
         runtimeTypeUses: runtimeTypeUses,
         isFunctionApplyUsed: backendUsage.isFunctionApplyUsed,
         isMirrorsUsed: backendUsage.isMirrorsUsed,

pkg/compiler/lib/src/kernel/dart2js_target.dart

@@ -131,7 +131,9 @@ class Dart2jsTarget extends Target {
   @override
   bool allowPlatformPrivateLibraryAccess(Uri importer, Uri imported) =>
       super.allowPlatformPrivateLibraryAccess(importer, imported) ||
-      maybeEnableNative(importer);
+      maybeEnableNative(importer) ||
+      (importer.scheme == 'package' &&
+          importer.path.startsWith('dart2js_runtime_metrics/'));
 
   @override
   bool enableNative(Uri uri) => maybeEnableNative(uri);
@@ -235,6 +237,7 @@ class Dart2jsTarget extends Target {
 // compile-platform should just specify which libraries to compile instead.
 const _requiredLibraries = const <String, List<String>>{
   'dart2js': const <String>[
+    'dart:_dart2js_runtime_metrics',
     'dart:_foreign_helper',
     'dart:_interceptors',
     'dart:_internal',
@@ -258,6 +261,7 @@ const _requiredLibraries = const <String, List<String>>{
     'dart:web_sql',
   ],
   'dart2js_server': const <String>[
+    'dart:_dart2js_runtime_metrics',
     'dart:_foreign_helper',
     'dart:_interceptors',
     'dart:_internal',

pkg/dart2js_runtime_metrics/CHANGELOG.md

@@ -0,0 +1,3 @@
+## 0.1.0
+
+- Initial version.

pkg/dart2js_runtime_metrics/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2021, the Dart project authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

pkg/dart2js_runtime_metrics/README.md

@@ -0,0 +1,13 @@
+☠☠ **Warning: This package is experimental and may be removed in a future
+version of Dart.** ☠☠
+
+`dart2js` can generate extra code to measure certain activities.
+This library provides access to the measurements at runtime.
+
+An application might make timings and other measurements and report them back to
+a server in order to collect information on how the application is working in
+production. The APIs in this library provide access to measurements that require
+help from dart2js. For example, `startupMetrics` accesses measurements of
+activities that happen as the program is loaded, before `main()`.
+
+The APIs are stubbed so that dummy values are returned on the VM and dartdevc.

pkg/dart2js_runtime_metrics/analysis_options.yaml

@@ -0,0 +1,5 @@
+analyzer:
+  errors:
+    import_internal_library: ignore
+  strong-mode:
+    implicit-casts: false

pkg/dart2js_runtime_metrics/lib/_startup_metrics_dart2js.dart

@@ -0,0 +1,5 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'dart:_dart2js_runtime_metrics' show startupMetrics;

pkg/dart2js_runtime_metrics/lib/_startup_metrics_dartdevc.dart

@@ -0,0 +1,12 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// A collection of metrics for events that happen before `main()` is entered.
+///
+/// The contents of the map depend on the platform. The map values are simple
+/// objects (strings, numbers, Booleans). There is always an entry for the key
+/// `'runtime'` with a [String] value.
+Map<String, Object> get startupMetrics {
+  return {'runtime': 'dartdevc'};
+}

pkg/dart2js_runtime_metrics/lib/_startup_metrics_unknown.dart

@@ -0,0 +1,12 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// A collection of metrics for events that happen before `main()` is entered.
+///
+/// The contents of the map depend on the platform. The map values are simple
+/// objects (strings, numbers, Booleans). There is always an entry for the key
+/// `'runtime'` with a [String] value.
+Map<String, Object> get startupMetrics {
+  return {'runtime': 'unknown'};
+}

pkg/dart2js_runtime_metrics/lib/_startup_metrics_vm.dart

@@ -0,0 +1,12 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// A collection of metrics for events that happen before `main()` is entered.
+///
+/// The contents of the map depend on the platform. The map values are simple
+/// objects (strings, numbers, Booleans). There is always an entry for the key
+/// `'runtime'` with a [String] value.
+Map<String, Object> get startupMetrics {
+  return {'runtime': 'vm'};
+}

pkg/dart2js_runtime_metrics/lib/startup_metrics.dart

@@ -0,0 +1,8 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export '_startup_metrics_unknown.dart'
+    if (dart.library._dart2js_runtime_metrics) '_startup_metrics_dart2js.dart'
+    if (dart.library.ffi) '_startup_metrics_vm.dart'
+    if (dart.library.js) '_startup_metrics_dartdevc.dart';

pkg/dart2js_runtime_metrics/pubspec.yaml

@@ -0,0 +1,18 @@
+name: dart2js_runtime_metrics
+# This package is not intended for consumption on pub.dev. DO NOT publish.
+publish_to: none
+version: 0.1.0
+repository: https://github.com/dart-lang/sdk/tree/master/pkg/dart2js_runtime_metrics
+description: >-
+  `dart2js` can generate extra code to measure certain activities.
+  This library provides access to the measurements at runtime.
+
+environment:
+  # Restrict the upper bound so that we can remove support for this in
+  # a later version of the SDK without it being a breaking change.
+  sdk: ">=2.14.0 <2.15.0"
+
+dev_dependencies:
+  # Unpublished packages that can be used via path dependency
+  expect:
+    path: ../expect

pkg/dart2js_runtime_metrics/test/startup_metrics_test.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:dart2js_runtime_metrics/startup_metrics.dart';
+import 'package:expect/expect.dart';
+
+void main() {
+  Map<String, Object> metrics = startupMetrics;
+
+  print('metrics: $metrics');
+
+  String expectedRuntime;
+  if (1.0 is! int) {
+    expectedRuntime = 'vm';
+  } else if (ClassWithLongName().toString().contains('minified:')) {
+    // dart2js minified: "Instance of 'minified:xy'".
+    expectedRuntime = 'dart2js';
+  } else if ('$main' == "Closure 'main'") {
+    // dart2js non-minified.
+    expectedRuntime = 'dart2js';
+  } else if ('$main'.startsWith('Closure: () => void from: function main()')) {
+    expectedRuntime = 'dartdevc';
+  } else {
+    throw 'Cannot feature-test current runtime:'
+        '\nmetrics = $metrics\n main = $main';
+  }
+
+  Expect.isTrue(metrics.containsKey('runtime'), "Has 'runtime' key: $metrics");
+  Expect.equals(expectedRuntime, metrics['runtime'],
+      "Expected 'runtime: $expectedRuntime': $metrics");
+
+  if (expectedRuntime == 'dart2js') {
+    Expect.isTrue(metrics.containsKey('callMainMs'));
+    return;
+  }
+
+  if (expectedRuntime == 'dartdevc') {
+    Expect.equals(1, metrics.length);
+    return;
+  }
+
+  if (expectedRuntime == 'vm') {
+    Expect.equals(1, metrics.length);
+    return;
+  }
+
+  throw 'Should not get here.';
+}
+
+class ClassWithLongName {}

pkg/front_end/test/spell_checking_list_common.txt

@@ -1866,6 +1866,8 @@ met
 metadata
 method
 methods
+metric
+metrics
 microseconds
 microtask
 mid

pkg/js_runtime/lib/shared/embedded_names.dart

@@ -179,6 +179,9 @@ const DEFERRED_INITIALIZED = 'deferredInitialized';
 /// This embedded global is used for --experiment-new-rti.
 const RTI_UNIVERSE = 'typeUniverse';
 
+/// An embedded global used to collect and access startup metrics.
+const STARTUP_METRICS = 'sm';
+
 /// Names that are supported by [JS_GET_NAME].
 // TODO(herhut): Make entries lower case (as in fields) and find a better name.
 enum JsGetName {

sdk/lib/_internal/js_runtime/lib/dart2js_runtime_metrics.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library dart2js_runtime_metrics;
+
+import 'dart:_js_helper' show fillLiteralMap, rawStartupMetrics;
+
+/// A collection of metrics for events that happen before `main()` is entered.
+///
+/// The contents of the map depend on the platform. The map values are simple
+/// objects (strings, numbers, Booleans). There is always an entry for the key
+/// `'runtime'` with a [String] value.
+///
+/// This implementation for dart2js has the content (subject to change):
+///
+/// - `runtime`: `'dart2js'`
+///
+/// - `firstMs`:  first performance.now() reading in the main.dart.js file.
+///
+/// - `dartMainProgramMs`: performance.now() immediately inside the function
+///    wrapping all the Dart code
+///
+/// - `callMainMs`: performance.now() just before calling main()
+///
+/// The injected code uses `Date.now()` if `performance.now()` is not defined.
+Map<String, Object> get startupMetrics {
+  final Map<String, Object> result = {'runtime': 'dart2js'};
+  final raw = rawStartupMetrics();
+  fillLiteralMap(raw, result);
+  return result;
+}

sdk/lib/_internal/js_runtime/lib/js_helper.dart

@@ -21,6 +21,7 @@ import 'dart:_js_embedded_names'
         JsGetName,
         LEAF_TAGS,
         NATIVE_SUPERCLASS_TAG_NAME,
+        STARTUP_METRICS,
         STATIC_FUNCTION_NAME_PROPERTY_NAME,
         TearOffParametersPropertyNames;
 
@@ -3005,3 +3006,7 @@ void assertInteropArgs(List<Object?> args) {
   assert(args.every((arg) => arg is! Function || isJSFunction(arg)),
       'Dart function requires `allowInterop` to be passed to JavaScript.');
 }
+
+Object? rawStartupMetrics() {
+  return JS('JSArray', '#.a', JS_EMBEDDED_GLOBAL('', STARTUP_METRICS));
+}

sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart

@@ -179,6 +179,9 @@ const DEFERRED_INITIALIZED = 'deferredInitialized';
 /// This embedded global is used for --experiment-new-rti.
 const RTI_UNIVERSE = 'typeUniverse';
 
+/// An embedded global used to collect and access startup metrics.
+const STARTUP_METRICS = 'sm';
+
 /// Names that are supported by [JS_GET_NAME].
 // TODO(herhut): Make entries lower case (as in fields) and find a better name.
 enum JsGetName {

sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart

@@ -153,6 +153,11 @@ const Map<String, LibraryInfo> libraries = const {
       categories: "", documented: false, platforms: DART2JS_PLATFORM),
   "_rti": const LibraryInfo("_internal/js_runtime/lib/rti.dart",
       categories: "", documented: false, platforms: DART2JS_PLATFORM),
+  "_dart2js_runtime_metrics": const LibraryInfo(
+      "_internal/js_runtime/lib/dart2js_runtime_metrics.dart",
+      categories: "",
+      documented: false,
+      platforms: DART2JS_PLATFORM),
   "_interceptors": const LibraryInfo(
       "_internal/js_runtime/lib/interceptors.dart",
       categories: "",

sdk/lib/libraries.json

@@ -235,6 +235,9 @@
       "web_sql": {
         "uri": "web_sql/dart2js/web_sql_dart2js.dart"
       },
+      "_dart2js_runtime_metrics": {
+        "uri": "_internal/js_runtime/lib/dart2js_runtime_metrics.dart"
+      },
       "_internal": {
         "uri": "internal/internal.dart",
         "patches": "_internal/js_runtime/lib/internal_patch.dart"
@@ -338,6 +341,9 @@
         "uri": "internal/internal.dart",
         "patches": "_internal/js_runtime/lib/internal_patch.dart"
       },
+      "_dart2js_runtime_metrics": {
+        "uri": "_internal/js_runtime/lib/dart2js_runtime_metrics.dart"
+      },
       "_js_helper": {
         "uri": "_internal/js_runtime/lib/js_helper.dart"
       },
@@ -477,4 +483,4 @@
       }
     }
   }
-}
+}

sdk/lib/libraries.yaml

@@ -233,6 +233,9 @@ dart2js:
     web_sql:
       uri: "web_sql/dart2js/web_sql_dart2js.dart"
 
+    _dart2js_runtime_metrics:
+      uri: "_internal/js_runtime/lib/dart2js_runtime_metrics.dart"
+
     _internal:
       uri: "internal/internal.dart"
       patches: "_internal/js_runtime/lib/internal_patch.dart"
@@ -334,6 +337,9 @@ dart2js_server:
       uri: "internal/internal.dart"
       patches: "_internal/js_runtime/lib/internal_patch.dart"
 
+    _dart2js_runtime_metrics:
+      uri: "_internal/js_runtime/lib/dart2js_runtime_metrics.dart"
+
     _js_helper:
       uri: "_internal/js_runtime/lib/js_helper.dart"