Benchmark for semantic overhead during transitions (#10678)

* Benchmark for semantic overhead during transitions

* review comments

dev/devicelab/bin/tasks/flutter_gallery__transition_perf_with_semantics.dart

diff --git a/dev/devicelab/bin/tasks/flutter_gallery__transition_perf_with_semantics.dart b/dev/devicelab/bin/tasks/flutter_gallery__transition_perf_with_semantics.dart
new file mode 100644
index 0000000..27c6171
--- /dev/null
+++ b/dev/devicelab/bin/tasks/flutter_gallery__transition_perf_with_semantics.dart
@@ -0,0 +1,29 @@
+// Copyright 2017 The Chromium 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 'dart:async';
+
+import 'package:flutter_devicelab/tasks/gallery.dart';
+import 'package:flutter_devicelab/framework/adb.dart';
+import 'package:flutter_devicelab/framework/framework.dart';
+
+Future<Null> main() async {
+  deviceOperatingSystem = DeviceOperatingSystem.android;
+  await task(() async {
+    final TaskResult withoutSemantics = await createGalleryTransitionTest()();
+    final TaskResult withSemantics = await createGalleryTransitionTest(semanticsEnabled: true)();
+
+    final List<String> benchmarkScoreKeys = <String>[];
+    final Map<String, dynamic> data = <String, dynamic>{};
+    for (String key in withSemantics.benchmarkScoreKeys) {
+      final String deltaKey = 'delta_$key';
+      data[deltaKey] = withSemantics.data[key] - withoutSemantics.data[key];
+      data['semantics_$key'] = withSemantics.data[key];
+      data[key] = withoutSemantics.data[key];
+      benchmarkScoreKeys.add(deltaKey);
+    }
+
+    return new TaskResult.success(data, benchmarkScoreKeys: benchmarkScoreKeys);
+  });
+}

dev/devicelab/lib/tasks/gallery.dart

diff --git a/dev/devicelab/lib/tasks/gallery.dart b/dev/devicelab/lib/tasks/gallery.dart
index 6a36e00..b073003 100644
--- a/dev/devicelab/lib/tasks/gallery.dart
+++ b/dev/devicelab/lib/tasks/gallery.dart
@@ -12,12 +12,16 @@
 import '../framework/ios.dart';
 import '../framework/utils.dart';
 
-TaskFunction createGalleryTransitionTest() {
-  return new GalleryTransitionTest();
+TaskFunction createGalleryTransitionTest({ bool semanticsEnabled: false }) {
+  return new GalleryTransitionTest(semanticsEnabled: semanticsEnabled);
 }
 
 class GalleryTransitionTest {
 
+  GalleryTransitionTest({ this.semanticsEnabled: false });
+
+  final bool semanticsEnabled;
+
   Future<TaskResult> call() async {
     final Device device = await devices.workingDevice;
     await device.unlock();
@@ -33,11 +37,15 @@
         await flutter('build', options: <String>['ios', '--profile']);
       }
 
+      final String testDriver = semanticsEnabled
+          ? 'transitions_perf_with_semantics.dart'
+          : 'transitions_perf.dart';
+
       await flutter('drive', options: <String>[
         '--profile',
         '--trace-startup',
         '-t',
-        'test_driver/transitions_perf.dart',
+        'test_driver/$testDriver',
         '-d',
         deviceId,
       ]);

dev/devicelab/manifest.yaml

diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
index a67b889..a8fab3f 100644
--- a/dev/devicelab/manifest.yaml
+++ b/dev/devicelab/manifest.yaml
@@ -274,6 +274,14 @@
     stage: devicelab
     required_agent_capabilities: ["linux/android"]
 
+  flutter_gallery__transition_perf_with_semantics:
+    description: >
+      Measures the delta in performance of screen transitions without and
+      with semantics enabled.
+    stage: devicelab
+    required_agent_capabilities: ["linux/android"]
+    flaky: true
+
   flutter_gallery__memory_nav:
     description: >
       Measures memory usage after repeated navigation in Gallery.