Add cull opacity perf test to device lab (#25381)

For https://github.com/flutter/flutter/issues/24712

This test verifies that https://github.com/flutter/engine/pull/6923 will speedup the average rasterize time of this test from ~150ms to ~10ms

Please see non-auto-generated files in https://github.com/flutter/flutter/pull/25381/commits/37b21d9fb4756a8d8d12ae0def1d0640740c8818

dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart

diff --git a/dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart
new file mode 100644
index 0000000..ffab86c
--- /dev/null
+++ b/dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart
@@ -0,0 +1,14 @@
+// Copyright 2018 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/perf_tests.dart';
+import 'package:flutter_devicelab/framework/adb.dart';
+import 'package:flutter_devicelab/framework/framework.dart';
+
+Future<void> main() async {
+  deviceOperatingSystem = DeviceOperatingSystem.android;
+  await task(createCullOpacityPerfTest());
+}

dev/devicelab/lib/tasks/perf_tests.dart

diff --git a/dev/devicelab/lib/tasks/perf_tests.dart b/dev/devicelab/lib/tasks/perf_tests.dart
index 1356713..4594537 100644
--- a/dev/devicelab/lib/tasks/perf_tests.dart
+++ b/dev/devicelab/lib/tasks/perf_tests.dart
@@ -30,6 +30,14 @@
   ).run;
 }
 
+TaskFunction createCullOpacityPerfTest() {
+  return PerfTest(
+    '${flutterDirectory.path}/dev/benchmarks/macrobenchmarks',
+    'test_driver/cull_opacity_perf.dart',
+    'cull_opacity_perf',
+  ).run;
+}
+
 TaskFunction createFlutterGalleryStartupTest() {
   return StartupTest(
     '${flutterDirectory.path}/examples/flutter_gallery',

dev/devicelab/manifest.yaml

diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
index 649df48..f100596 100644
--- a/dev/devicelab/manifest.yaml
+++ b/dev/devicelab/manifest.yaml
@@ -112,6 +112,13 @@
     stage: devicelab
     required_agent_capabilities: ["mac/android"]
 
+  cull_opacity_perf__timeline_summary:
+    description: >
+      Measures the runtime performance of culling opacity widgets on Android.
+    stage: devicelab
+    required_agent_capabilities: ["mac/android"]
+    flaky: true # mark a new test as flaky
+
   flavors_test:
     description: >
       Checks that flavored builds work on Android.