Reland Add UI Benchmarks (#143542) (#143799)

Re-lands https://github.com/flutter/flutter/pull/143542 (which is part 1 of https://github.com/flutter/flutter/pull/138481)

The filename was wrong ðŸ«

dev/benchmarks/microbenchmarks/lib/foundation/observer_list_bench.dart

@@ -0,0 +1,181 @@
+// Copyright 2014 The Flutter Authors. 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:flutter/animation.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../common.dart';
+
+const int _kNumIterationsList = 2 << 14;
+const int _kNumIterationsHashed = 2 << 19;
+const int _kNumWarmUp = 2 << 6;
+const List<int> callbackCounts = <int>[1, 10, 100, 500];
+
+class TestAnimationController extends AnimationController {
+  TestAnimationController() : super(vsync: const TestVSync());
+
+  @override
+  void notifyListeners() => super.notifyListeners();
+}
+
+void main() {
+  assert(false,
+      "Don't run benchmarks in debug mode! Use 'flutter run --release'.");
+
+  final BenchmarkResultPrinter printer = BenchmarkResultPrinter();
+
+  void runNotifiyListenersLoopWithObserverList(
+    int totalIterations, {
+    bool failRemoval = false,
+    bool addResult = true,
+  }) {
+    final String suffix = failRemoval ? 'removalFail' : 'removalSuccess';
+    final String name = 'notifyListeners:ObserverList:$suffix';
+
+    void miss() {}
+
+    for (final int callbackCount in callbackCounts) {
+      final int iterations = totalIterations ~/ callbackCount;
+
+      final ObserverList<VoidCallback> observerList =
+          ObserverList<VoidCallback>();
+      for (int i = 0; i < callbackCount; ++i) {
+        observerList.add(
+          switch (failRemoval) {
+            false => () {
+                final VoidCallback first =
+                    (observerList.iterator..moveNext()).current;
+
+                observerList.remove(first);
+                observerList.add(first);
+              },
+            true => () => observerList.remove(miss),
+          },
+        );
+      }
+
+      final Stopwatch watch = Stopwatch()..start();
+
+      for (int i = 0; i < iterations; ++i) {
+        final List<VoidCallback> list = observerList.toList(growable: false);
+        for (final VoidCallback cb in list) {
+          if (observerList.contains(cb)) {
+            cb();
+          }
+        }
+      }
+
+      watch.stop();
+
+      if (addResult) {
+        printer.addResult(
+          description: '$name ($callbackCount callbacks)',
+          value: watch.elapsedMicroseconds / iterations,
+          unit: 'µs per iteration',
+          name: '$name$callbackCount',
+        );
+      }
+    }
+  }
+
+  void runNotifiyListenersLoopWithHashedObserverList(
+    int totalIterations, {
+    bool addResult = true,
+  }) {
+    const String name = 'notifyListeners:HashedObserverList';
+
+    for (final int callbackCount in callbackCounts) {
+      final int iterations = totalIterations ~/ callbackCount;
+
+      final HashedObserverList<VoidCallback> observerList =
+          HashedObserverList<VoidCallback>();
+      for (int i = 0; i < callbackCount; ++i) {
+        observerList.add(() {
+          final VoidCallback first =
+              (observerList.iterator..moveNext()).current;
+
+          observerList.remove(first);
+          observerList.add(first);
+        });
+      }
+
+      final Stopwatch watch = Stopwatch()..start();
+
+      for (int i = 0; i < iterations; ++i) {
+        final List<VoidCallback> list = observerList.toList(growable: false);
+        for (final VoidCallback cb in list) {
+          if (observerList.contains(cb)) {
+            cb();
+          }
+        }
+      }
+
+      watch.stop();
+
+      if (addResult) {
+        printer.addResult(
+          description: '$name ($callbackCount callbacks)',
+          value: watch.elapsedMicroseconds / iterations,
+          unit: 'µs per iteration',
+          name: '$name$callbackCount',
+        );
+      }
+    }
+  }
+
+  void runNotifiyListenersLoopWithAnimationController(
+    int totalIterations, {
+    bool addResult = true,
+  }) {
+    const String name = 'notifyListeners:AnimationController';
+
+    for (final int callbackCount in callbackCounts) {
+      final int iterations = totalIterations ~/ callbackCount;
+
+      final TestAnimationController controller = TestAnimationController();
+      for (int i = 0; i < callbackCount; ++i) {
+        late final VoidCallback cb;
+        cb = () {
+          controller.removeListener(cb);
+          controller.addListener(cb);
+        };
+        controller.addListener(cb);
+      }
+
+      final Stopwatch watch = Stopwatch()..start();
+
+      for (int i = 0; i < iterations; ++i) {
+        controller.notifyListeners();
+      }
+
+      watch.stop();
+
+      if (addResult) {
+        printer.addResult(
+          description: '$name ($callbackCount callbacks)',
+          value: watch.elapsedMicroseconds / iterations,
+          unit: 'µs per iteration',
+          name: '$name$callbackCount',
+        );
+      }
+    }
+  }
+
+  runNotifiyListenersLoopWithObserverList(_kNumWarmUp, addResult: false);
+  runNotifiyListenersLoopWithObserverList(_kNumIterationsList);
+
+  runNotifiyListenersLoopWithObserverList(_kNumWarmUp,
+      failRemoval: true, addResult: false);
+  runNotifiyListenersLoopWithObserverList(_kNumIterationsList,
+      failRemoval: true);
+
+  runNotifiyListenersLoopWithHashedObserverList(_kNumWarmUp, addResult: false);
+  runNotifiyListenersLoopWithHashedObserverList(_kNumIterationsHashed);
+
+  runNotifiyListenersLoopWithAnimationController(_kNumWarmUp, addResult: false);
+  runNotifiyListenersLoopWithAnimationController(_kNumIterationsHashed);
+
+  printer.printToStdout();
+}

dev/devicelab/lib/tasks/microbenchmarks.dart

@@ -57,6 +57,7 @@ TaskFunction createMicrobenchmarkTask({
       ...await runMicrobench('lib/foundation/all_elements_bench.dart'),
       ...await runMicrobench('lib/foundation/change_notifier_bench.dart'),
       ...await runMicrobench('lib/foundation/clamp.dart'),
+      ...await runMicrobench('lib/foundation/observer_list_bench.dart'),
       ...await runMicrobench('lib/foundation/platform_asset_bundle.dart'),
       ...await runMicrobench('lib/foundation/standard_message_codec_bench.dart'),
       ...await runMicrobench('lib/foundation/standard_method_codec_bench.dart'),