Add a class to start and stop a Chrome process.

lib/src/runner/browser/chrome.dart

Index: lib/src/runner/browser/chrome.dart
diff --git a/lib/src/runner/browser/chrome.dart b/lib/src/runner/browser/chrome.dart
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+++ b/lib/src/runner/browser/chrome.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 unittest.runner.browser.chrome;
+
+import 'dart:async';
+import 'dart:io';
+
+import '../../util/io.dart';
+
+// TODO(nweiz): move this into its own package?
+// TODO(nweiz): support other browsers.
+/// A class for running an instance of Chrome.
+///
+/// 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 Chrome {
+  /// The underlying process.
+  Process _process;
+
+  /// The temporary directory used as the browser's user data dir.
+  ///
+  /// A new data dir is created for each run to ensure that they're
+  /// well-isolated.
+  String _dir;
+
+  /// A future that completes when the browser exits.
+  ///
+  /// If there's a problem starting or running the browser, this will complete
+  /// with an error.
+  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 Chrome open to the given [url], which may be a
+  /// [Uri] or a [String].
+  ///
+  /// If [executable] is passed, it's used as the Chrome executable. Otherwise
+  /// `"google-chrome"` will be looked up on the system PATH.
+  Chrome(url, {String executable}) {
+    if (executable == null) executable = "google-chrome";
+
+    // 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.
+    withTempDir((dir) {
+      _dir = dir;
+      return Process.start(executable, [
+        "--user-data-dir=$_dir",
+        url.toString(),
+        "--disable-extensions",
+        "--disable-popup-blocking",
+        "--bwsi",
+        "--no-first-run"
+      ]).then((process) {
+        _process = process;
+        _onProcessStartedCompleter.complete();
+
+        // TODO(nweiz): the browser's standard output is almost always useless
+        // noise, but we should allow the user to opt in to seeing it.
+        return _process.exitCode;
+      });
+    }).then((exitCode) {
+      if (exitCode != 0) throw "Chrome failed with exit code $exitCode.";
+    }).then(_onExitCompleter.complete)
+        .catchError(_onExitCompleter.completeError);
+  }
+
+  /// Kills the browser process.
+  ///
+  /// Returns the same [Future] as [onExit], except that it won't emit
+  /// exceptions.
+  Future close() {
+    _onProcessStarted.then((_) => _process.kill());
+
+    // Swallow exceptions. The user should explicitly use [onExit] for these.
+    return onExit.catchError((_) {});
+  }
+}