Add custom test plugin that supports screenshot tests

.cirrus.yml

@@ -36,9 +36,12 @@ task:
         cd $ENGINE_PATH/src
         ./flutter/testing/run_tests.sh host_debug_unopt
       test_web_engine_script: |
+        google-chrome --version
+        cd $ENGINE_PATH/src/flutter/web_sdk/web_engine_tester
+        $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/pub get
         cd $ENGINE_PATH/src/flutter/lib/web_ui
         $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/pub get
-        $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/dart dev/test.dart
+        CHROME_NO_SANDBOX=true $ENGINE_PATH/src/out/host_debug_unopt/dart-sdk/bin/dart dev/test.dart
       fetch_framework_script: |
         mkdir -p $FRAMEWORK_PATH
         cd $FRAMEWORK_PATH

lib/web_ui/.gitignore

@@ -0,0 +1 @@
+build/

lib/web_ui/build.yaml

@@ -0,0 +1,11 @@
+targets:
+  $default:
+    builders:
+      build_web_compilers|entrypoint:
+        options:
+          compiler: dart2js
+          dart2js_args:
+            - --no-minify
+            - --enable-asserts
+        generate_for:
+          - test/**.dart

lib/web_ui/dev/environment.dart

@@ -0,0 +1,175 @@
+// Copyright 2013 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 'dart:io' as io;
+import 'package:args/args.dart' as args;
+import 'package:path/path.dart' as pathlib;
+
+/// Contains various environment variables, such as common file paths and command-line options.
+Environment get environment {
+  if (Environment.commandLineArguments == null) {
+    io.stderr.writeln('Command-line options not passed to Environment.');
+    io.exit(1);
+  }
+  if (_environment == null) {
+    _environment = Environment();
+  }
+  return _environment;
+}
+Environment _environment;
+
+args.ArgParser get _argParser {
+  return args.ArgParser()
+    ..addMultiOption(
+      'target',
+      abbr: 't',
+      help: 'The path to the target to run. When omitted, runs all targets.',
+    )
+    ..addMultiOption(
+      'shard',
+      abbr: 's',
+      help: 'The category of tasks to run.',
+    )
+    ..addFlag(
+      'debug',
+      help: 'Pauses the browser before running a test, giving you an '
+        'opportunity to add breakpoints or inspect loaded code before '
+        'running the code.',
+    );
+}
+
+/// Contains various environment variables, such as common file paths and command-line options.
+class Environment {
+  /// Command-line arguments.
+  static List<String> commandLineArguments;
+
+  factory Environment() {
+    if (commandLineArguments == null) {
+      io.stderr.writeln('Command-line arguments not set.');
+      io.exit(1);
+    }
+
+    final args.ArgResults options = _argParser.parse(commandLineArguments);
+    final List<String> shards = options['shard'];
+    final bool isDebug = options['debug'];
+    final List<String> targets = options['target'];
+
+    final io.File self = io.File.fromUri(io.Platform.script);
+    final io.Directory webUiRootDir = self.parent.parent;
+    final io.Directory engineSrcDir = webUiRootDir.parent.parent.parent;
+    final io.Directory outDir = io.Directory(pathlib.join(engineSrcDir.path, 'out'));
+    final io.Directory hostDebugUnoptDir = io.Directory(pathlib.join(outDir.path, 'host_debug_unopt'));
+    final String dartExecutable = pathlib.canonicalize(io.File(_which(io.Platform.executable)).absolute.path);
+    final io.Directory dartSdkDir = io.File(dartExecutable).parent.parent;
+
+    // Googlers frequently have their Dart SDK misconfigured for open-source projects. Let's help them out.
+    if (dartExecutable.startsWith('/usr/lib/google-dartlang')) {
+      io.stderr.writeln('ERROR: Using unsupported version of the Dart SDK: $dartExecutable');
+      io.exit(1);
+    }
+
+    return Environment._(
+      self: self,
+      webUiRootDir: webUiRootDir,
+      engineSrcDir: engineSrcDir,
+      outDir: outDir,
+      hostDebugUnoptDir: hostDebugUnoptDir,
+      dartExecutable: dartExecutable,
+      dartSdkDir: dartSdkDir,
+      requestedShards: shards,
+      isDebug: isDebug,
+      targets: targets,
+    );
+  }
+
+  Environment._({
+    this.self,
+    this.webUiRootDir,
+    this.engineSrcDir,
+    this.outDir,
+    this.hostDebugUnoptDir,
+    this.dartSdkDir,
+    this.dartExecutable,
+    this.requestedShards,
+    this.isDebug,
+    this.targets,
+  });
+
+  /// The Dart script that's currently running.
+  final io.File self;
+
+  /// Path to the "web_ui" package sources.
+  final io.Directory webUiRootDir;
+
+  /// Path to the engine's "src" directory.
+  final io.Directory engineSrcDir;
+
+  /// Path to the engine's "out" directory.
+  ///
+  /// This is where you'll find the ninja output, such as the Dart SDK.
+  final io.Directory outDir;
+
+  /// The "host_debug_unopt" build of the Dart SDK.
+  final io.Directory hostDebugUnoptDir;
+
+  /// The root of the Dart SDK.
+  final io.Directory dartSdkDir;
+
+  /// The "dart" executable file.
+  final String dartExecutable;
+
+  /// Shards specified on the command-line.
+  final List<String> requestedShards;
+
+  /// Whether to start the browser in debug mode.
+  ///
+  /// In this mode the browser pauses before running the test to allow
+  /// you set breakpoints or inspect the code.
+  final bool isDebug;
+
+  /// Paths to targets to run, e.g. a single test.
+  final List<String> targets;
+
+  /// The "pub" executable file.
+  String get pubExecutable => pathlib.join(dartSdkDir.path, 'bin', 'pub');
+
+  /// The "dart2js" executable file.
+  String get dart2jsExecutable => pathlib.join(dartSdkDir.path, 'bin', 'dart2js');
+
+  /// Path to where github.com/flutter/engine is checked out inside the engine workspace.
+  io.Directory get flutterDirectory => io.Directory(pathlib.join(engineSrcDir.path, 'flutter'));
+  io.Directory get webSdkRootDir => io.Directory(pathlib.join(
+    flutterDirectory.path,
+    'web_sdk',
+  ));
+
+  /// Path to the "web_engine_tester" package.
+  io.Directory get goldenTesterRootDir => io.Directory(pathlib.join(
+    webSdkRootDir.path,
+    'web_engine_tester',
+  ));
+
+  /// Path to the "build" directory, generated by "package:build_runner".
+  ///
+  /// This is where compiled output goes.
+  io.Directory get webUiBuildDir => io.Directory(pathlib.join(
+    webUiRootDir.path,
+    'build',
+  ));
+
+  /// Path to the ".dart_tool" directory, generated by various Dart tools.
+  io.Directory get webUiDartToolDir => io.Directory(pathlib.join(
+    webUiRootDir.path,
+    '.dart_tool',
+  ));
+}
+
+String _which(String executable) {
+  final io.ProcessResult result = io.Process.runSync('which', <String>[executable]);
+  if (result.exitCode != 0) {
+    io.stderr.writeln(result.stderr);
+    io.exit(result.exitCode);
+  }
+  return result.stdout;
+}