New benchmark: Gesture semantics (#35232)

* Add semanticsEnabled to widgetBenchmark
* Add button_matrix_app and gesture benchmark

dev/benchmarks/microbenchmarks/README.md

@@ -6,6 +6,7 @@ these:
 
 ```
 flutter run --release lib/gestures/velocity_tracker_data.dart
+flutter run --release lib/gestures/gesture_detector_bench.dart
 flutter run --release lib/stocks/animation_bench.dart
 flutter run --release lib/stocks/build_bench.dart
 flutter run --release lib/stocks/layout_bench.dart

dev/benchmarks/microbenchmarks/lib/gestures/apps/button_matrix_app.dart

@@ -0,0 +1,52 @@
+// Copyright 2019 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/material.dart';
+
+class ButtonMatrixApp extends StatefulWidget {
+  @override
+  ButtonMatrixAppState createState() => ButtonMatrixAppState();
+}
+
+class ButtonMatrixAppState extends State<ButtonMatrixApp> {
+
+  int count = 1;
+  int increment = 1;
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        appBar: AppBar(
+          title: Text('Count: $count'),
+          actions: <Widget>[
+            FlatButton(
+              onPressed: () => setState(() { count += increment; }),
+              child: Text('Add $increment'),
+            ),
+          ],
+        ),
+        body: Row(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: List<Widget>.filled(
+            3,
+            Column(
+              children: List<Widget>.filled(
+                10,
+                FlatButton(
+                  child: const Text('Faster'),
+                  onPressed: () => setState(() { increment += 1; }),
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+void main() {
+  runApp(ButtonMatrixApp());
+}

dev/benchmarks/microbenchmarks/lib/gestures/gesture_detector_bench.dart

@@ -0,0 +1,52 @@
+// Copyright 2019 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/gestures.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../common.dart';
+import './apps/button_matrix_app.dart' as button_matrix;
+
+const int _kNumWarmUpIters = 20;
+const int _kNumIters = 300;
+
+Future<void> main() async {
+  assert(false, "Don't run benchmarks in checked mode! Use 'flutter run --release'.");
+  final Stopwatch watch = Stopwatch();
+  print('GestureDetector semantics benchmark...');
+
+  await benchmarkWidgets((WidgetTester tester) async {
+    button_matrix.main();
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+
+    Future<void> iter() async {
+      // Press a button to update the screen
+      await tester.tapAt(const Offset(760.0, 30.0));
+      await tester.pump();
+    }
+
+    // Warm up runs get the app into steady state, making benchmark
+    // results more credible
+    for (int i = 0; i < _kNumWarmUpIters; i += 1) {
+      await iter();
+    }
+    await tester.pumpAndSettle();
+
+    watch.start();
+    for (int i = 0; i < _kNumIters; i += 1) {
+      await iter();
+    }
+    watch.stop();
+  }, semanticsEnabled: true);
+
+  final BenchmarkResultPrinter printer = BenchmarkResultPrinter();
+  printer.addResult(
+    description: 'GestureDetector',
+    value: watch.elapsedMicroseconds / _kNumIters,
+    unit: 'µs per iteration',
+    name: 'gesture_detector_bench',
+  );
+  printer.printToStdout();
+}

dev/devicelab/lib/tasks/microbenchmarks.dart

@@ -53,6 +53,7 @@ TaskFunction createMicrobenchmarkTask() {
     allResults.addAll(await _runMicrobench('lib/stocks/build_bench.dart'));
     allResults.addAll(await _runMicrobench('lib/geometry/rrect_contains_bench.dart'));
     allResults.addAll(await _runMicrobench('lib/gestures/velocity_tracker_bench.dart'));
+    allResults.addAll(await _runMicrobench('lib/gestures/gesture_detector_bench.dart'));
     allResults.addAll(await _runMicrobench('lib/stocks/animation_bench.dart'));
 
     return TaskResult.success(allResults, benchmarkScoreKeys: allResults.keys.toList());

packages/flutter_test/lib/src/widget_tester.dart

@@ -68,7 +68,7 @@ typedef WidgetTesterCallback = Future<void> Function(WidgetTester widgetTester);
 /// In general, timeouts are race conditions and cause flakes, so best practice
 /// is to avoid the use of timeouts in tests.
 ///
-/// If the `enableSemantics` parameter is set to `true`,
+/// If the `semanticsEnabled` parameter is set to `true`,
 /// [WidgetTester.ensureSemantics] will have been called before the tester is
 /// passed to the `callback`, and that handle will automatically be disposed
 /// after the callback is finished.
@@ -144,6 +144,11 @@ void testWidgets(
 /// If the callback is asynchronous, make sure you `await` the call
 /// to [benchmarkWidgets], otherwise it won't run!
 ///
+/// If the `semanticsEnabled` parameter is set to `true`,
+/// [WidgetTester.ensureSemantics] will have been called before the tester is
+/// passed to the `callback`, and that handle will automatically be disposed
+/// after the callback is finished.
+///
 /// Benchmarks must not be run in checked mode, because the performance is not
 /// representative. To avoid this, this function will print a big message if it
 /// is run in checked mode. Unit tests of this method pass `mayRunWithAsserts`,
@@ -165,7 +170,11 @@ void testWidgets(
 ///       });
 ///       exit(0);
 ///     }
-Future<void> benchmarkWidgets(WidgetTesterCallback callback, {bool mayRunWithAsserts = false}) {
+Future<void> benchmarkWidgets(
+  WidgetTesterCallback callback, {
+  bool mayRunWithAsserts = false,
+  bool semanticsEnabled = true,
+}) {
   assert(() {
     if (mayRunWithAsserts)
       return true;
@@ -186,9 +195,16 @@ Future<void> benchmarkWidgets(WidgetTesterCallback callback, {bool mayRunWithAss
   final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   assert(binding is! AutomatedTestWidgetsFlutterBinding);
   final WidgetTester tester = WidgetTester._(binding);
+  SemanticsHandle semanticsHandle;
+  if (semanticsEnabled == true) {
+    semanticsHandle = tester.ensureSemantics();
+  }
   tester._recordNumberOfSemanticsHandles();
   return binding.runTest(
-    () => callback(tester),
+    () async {
+      await callback(tester);
+      semanticsHandle?.dispose();
+    },
     tester._endOfTestVerifications,
   ) ?? Future<void>.value();
 }