[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/extension_mrpm_host_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/extension_mrpm_host_factory.h"
+
+#include "chrome/browser/media/router/extension_media_route_provider_manager_host.h"
+#include "chrome/browser/media/router/media_router_impl.h"
+#include "chrome/browser/media/router/media_router_impl_factory.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
+ExtensionMediaRouteProviderManagerHost*
+ExtensionMRPMHostFactory::GetMRPMHostForBrowserContext(
+    BrowserContext* context) {
+  DCHECK(context);
+
+  return static_cast<ExtensionMediaRouteProviderManagerHost*>(
+      GetInstance()->GetServiceForBrowserContext(context, true));
+}
+
+// static
+ExtensionMRPMHostFactory* ExtensionMRPMHostFactory::GetInstance() {
+  return Singleton<ExtensionMRPMHostFactory>::get();
+}
+
+ExtensionMRPMHostFactory::ExtensionMRPMHostFactory()
+    : BrowserContextKeyedServiceFactory(
+          "ExtensionMediaRouteProviderManagerHost",
+          BrowserContextDependencyManager::GetInstance()) {
+  DependsOn(MediaRouterImplFactory::GetInstance());
+}
+
+ExtensionMRPMHostFactory::~ExtensionMRPMHostFactory() {
+}
+
+KeyedService* ExtensionMRPMHostFactory::BuildServiceInstanceFor(
+    BrowserContext* context) const {
+  MediaRouterImpl* router =
+      MediaRouterImplFactory::GetMediaRouterForBrowserContext(context);
+  DCHECK(router);
+
+  auto* mrpm_host = new ExtensionMediaRouteProviderManagerHost(context, router);
+  router->SetMRPMHost(mrpm_host);
+  return mrpm_host;
+}
+
+BrowserContext* ExtensionMRPMHostFactory::GetBrowserContextToUse(
+    BrowserContext* context) const {
+  // This means MediaRouterImpl is available in incongnito contexts as well.
+  return chrome::GetBrowserContextOwnInstanceInIncognito(context);
+}
+
+}  // namespace media_router