[ddc] Stubbing package:dart2js_runtime_metrics

This allows the package to be discoverable across web backends

Change-Id: I7d870a7232543d3b719d47de1424017d7f578434
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/244261
Commit-Queue: Mark Zhou <markzipan@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>

pkg/dev_compiler/lib/src/kernel/target.dart

@@ -133,7 +133,9 @@ class DevCompilerTarget extends Target {
   @override
   bool allowPlatformPrivateLibraryAccess(Uri importer, Uri imported) =>
       super.allowPlatformPrivateLibraryAccess(importer, imported) ||
-      _allowedTestLibrary(importer);
+      _allowedTestLibrary(importer) ||
+      (importer.isScheme('package') &&
+          importer.path.startsWith('dart2js_runtime_metrics/'));
 
   @override
   bool get nativeExtensionExpectsString => false;

sdk/lib/_internal/js_dev_runtime/private/runtime_metrics.dart

@@ -0,0 +1,10 @@
+// Copyright (c) 2022, 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.
+
+// This file is a stub to allow dart:_dart2js_runtime_metrics to be discovered
+// across web contexts.
+
+get runtimeMetrics => throw UnimplementedError();
+
+get startupMetrics => throw UnimplementedError();

sdk/lib/libraries.json

@@ -433,6 +433,9 @@
       "_native_typed_data": {
         "uri": "_internal/js_dev_runtime/private/native_typed_data.dart"
       },
+      "_dart2js_runtime_metrics": {
+        "uri": "_internal/js_dev_runtime/private/runtime_metrics.dart"
+      },
       "async": {
         "uri": "async/async.dart",
         "patches": "_internal/js_dev_runtime/patch/async_patch.dart"

sdk/lib/libraries.yaml

@@ -399,6 +399,9 @@ dartdevc:
       _native_typed_data:
         uri: "_internal/js_dev_runtime/private/native_typed_data.dart"
 
+      _dart2js_runtime_metrics:
+        uri: "_internal/js_dev_runtime/private/runtime_metrics.dart"
+
       async:
         uri: "async/async.dart"
         patches: "_internal/js_dev_runtime/patch/async_patch.dart"