Add content shell support.

lib/src/runner/browser/content_shell.dart

Index: lib/src/runner/browser/content_shell.dart
diff --git a/lib/src/runner/browser/content_shell.dart b/lib/src/runner/browser/content_shell.dart
new file mode 100644
index 0000000000000000000000000000000000000000..875ba32607443607a79a305c8ebbf4fb69a3559d
--- /dev/null
+++ b/lib/src/runner/browser/content_shell.dart
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+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library test.runner.browser.content_shell;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+
+import '../../util/io.dart';
+import 'browser.dart';
+
+/// A class for running an instance of the Dartium content shell.
+///
+/// Most of the communication with the browser is expected to happen via HTTP,
+/// so this exposes a bare-bones API. The browser starts as soon as the class is
+/// constructed, and is killed when [close] is called.
+///
+/// Any errors starting or running the process are reported through [onExit].
+class ContentShell implements Browser {
+  /// The underlying process.
+  Process _process;
+
+  Future get onExit => _onExitCompleter.future;
+  final _onExitCompleter = new Completer();
+
+  /// A future that completes when the browser process has started.
+  ///
+  /// This is used to ensure that [close] works regardless of when it's called.
+  Future get _onProcessStarted => _onProcessStartedCompleter.future;
+  final _onProcessStartedCompleter = new Completer();
+
+  /// Starts a new instance of content shell open to the given [url], which may
+  /// be a [Uri] or a [String].
+  ///
+  /// If [executable] is passed, it's used as the content shell executable.
+  /// Otherwise the default executable name for the current OS will be used.
+  ContentShell(url, {String executable}) {
+    if (executable == null) executable = _defaultExecutable();
+
+    // Don't return a Future here because there's no need for the caller to wait
+    // for the process to actually start. They should just wait for the HTTP
+    // request instead.
+    Process.start(executable, ["--dump-render-tree", url.toString()],
+        environment: {"DART_FLAGS": "--checked"}).then((process) {
+      _process = process;
+      _onProcessStartedCompleter.complete();
+      return _process.exitCode;
+    }).then((exitCode) {
+      if (exitCode != 0) throw "Content shell failed with exit code $exitCode.";
+    }).then(_onExitCompleter.complete)
+        .catchError(_onExitCompleter.completeError);
+  }
+
+  Future close() {
+    _onProcessStarted.then((_) => _process.kill());
+
+    // Swallow exceptions. The user should explicitly use [onExit] for these.
+    return onExit.catchError((_) {});
+  }
+
+  /// Return the default executable for the current operating system.
+  String _defaultExecutable() =>
+      Platform.isWindows ? "content_shell.exe" : "content_shell";
+}