Add firefox support.

lib/src/runner/browser/chrome.dart

 // 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.chrome;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 
 import '../../util/io.dart';
+import 'browser.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 {
+class Chrome implements Browser {
   /// 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
@@ skipping 26 matching lines @@
         // 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((_) {});
   }
 
   /// Return the default executable for the current operating system.
   String _defaultExecutable() {
     if (Platform.isMacOS) {
@@ skipping 15 matching lines @@
 
       var path = p.join(prefix, suffix);
       if (new File(p.join(prefix, suffix)).existsSync()) return path;
     }
 
     // Fall back on looking it up on the path. This probably won't work, but at
     // least it will fail with a useful error message.
     return "chrome.exe";
   }
 }