Add support for running tests on Dartium.

lib/src/runner/browser/browser_manager.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.browser_manager;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:http_parser/http_parser.dart';
@@ skipping 46 matching lines @@
         var asyncError = RemoteException.deserialize(response["error"]);
         return new Future.error(
             new LoadException(path, asyncError.error),
             asyncError.stackTrace);
       }
 
       return new Suite(response["tests"].map((test) {
         var metadata = new Metadata.deserialize(test['metadata']);
         var testChannel = suiteChannel.virtualChannel(test['channel']);
         return new IframeTest(test['name'], metadata, testChannel);
-      }), path: path, platform: "Chrome");
+      }), path: path);
     });
   }
 }