Add layout tests for ServiceWorker's notificationclose event.

components/test_runner/test_runner.h

Index: components/test_runner/test_runner.h
diff --git a/components/test_runner/test_runner.h b/components/test_runner/test_runner.h
index a7add70f221e57400b84c9db1d0f4e87c56761e3..d9b08a18804b9e401a086659ae8453250848bfaf 100644
--- a/components/test_runner/test_runner.h
+++ b/components/test_runner/test_runner.h
@@ -590,6 +590,9 @@ class TestRunner : public WebTestRunner,
   // Simulates a click on a Web Notification.
   void SimulateWebNotificationClick(const std::string& title, int action_index);
 
+  // Simulates closing a Web Notification.
+  void SimulateWebNotificationClose(const std::string& title, bool by_user);
+
   // Speech recognition related functions.
   void AddMockSpeechRecognitionResult(const std::string& transcript,
                                       double confidence);