Push API: test that default notification is shown on Android when needed.

chrome/browser/push_messaging/push_messaging_service_observer.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/push_messaging/push_messaging_service_observer.h"
+
+#include "build/build_config.h"
+
+#if defined(OS_ANDROID)
+#include "chrome/browser/push_messaging/push_messaging_service_observer_android.h"
+#endif
+
+// static
+PushMessagingServiceObserver* PushMessagingServiceObserver::Create() {
+#if defined(OS_ANDROID)
+  return new PushMessagingServiceObserverAndroid();
+#endif
+  return nullptr;
+}