Add content shell support.

lib/src/runner/browser/server.dart

Index: lib/src/runner/browser/server.dart
diff --git a/lib/src/runner/browser/server.dart b/lib/src/runner/browser/server.dart
index 125c6ec1ee9f9c2c407ba110c2a0ea88db679a3f..67cead97be81560c4933e10d4fb0a827a70209e4 100644
--- a/lib/src/runner/browser/server.dart
+++ b/lib/src/runner/browser/server.dart
@@ -27,6 +27,7 @@ import 'browser_manager.dart';
 import 'compiler_pool.dart';
 import 'chrome.dart';
 import 'dartium.dart';
+import 'content_shell.dart';
 import 'firefox.dart';
 
 /// A server that serves JS-compiled tests to browsers.
@@ -349,6 +350,7 @@ void main() {
   Browser _newBrowser(Uri url, TestPlatform browser) {
     switch (browser) {
       case TestPlatform.dartium: return new Dartium(url);
+      case TestPlatform.contentShell: return new ContentShell(url);
       case TestPlatform.chrome: return new Chrome(url);
       case TestPlatform.firefox: return new Firefox(url);
       default: