[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_router_impl_factory.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/media/router/media_router_impl_factory.h"
+
+#include "chrome/browser/media/router/media_router_impl.h"
+#include "chrome/browser/profiles/incognito_helpers.h"
+#include "components/keyed_service/content/browser_context_dependency_manager.h"
+
+using content::BrowserContext;
+
+namespace media_router {
+
+// static
+MediaRouterImpl* MediaRouterImplFactory::GetMediaRouterForBrowserContext(
+    BrowserContext* context) {
+  DCHECK(context);
+  return static_cast<MediaRouterImpl*>(
+      GetInstance()->GetServiceForBrowserContext(context, true));
+}
+
+// static
+MediaRouterImplFactory* MediaRouterImplFactory::GetInstance() {
+  return Singleton<MediaRouterImplFactory>::get();
+}
+
+MediaRouterImplFactory::MediaRouterImplFactory()
+    : BrowserContextKeyedServiceFactory(
+          "MediaRouterImpl",
+          BrowserContextDependencyManager::GetInstance()) {
+}
+
+MediaRouterImplFactory::~MediaRouterImplFactory() {
+}
+
+KeyedService* MediaRouterImplFactory::BuildServiceInstanceFor(
+    BrowserContext* context) const {
+  return new MediaRouterImpl;
+}
+
+BrowserContext* MediaRouterImplFactory::GetBrowserContextToUse(
+    BrowserContext* context) const {
+  // This means MediaRouterImpl is available in incongnito contexts as well.
+  return chrome::GetBrowserContextOwnInstanceInIncognito(context);
+}
+
+}  // namespace media_router