Introduce HistoryClient interface

chrome/browser/history/chrome_history_client_factory.h

+// Copyright 2014 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.
+
+#ifndef CHROME_BROWSER_HISTORY_CHROME_HISTORY_CLIENT_FACTORY_H_
+#define CHROME_BROWSER_HISTORY_CHROME_HISTORY_CLIENT_FACTORY_H_
+
+#include "base/memory/singleton.h"
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+
+class ChromeHistoryClient;
+class Profile;
+
+// Singleton that owns all ChromeHistoryClients and associates them with
+// Profiles.
+class ChromeHistoryClientFactory : public BrowserContextKeyedServiceFactory {
+ public:
+  static ChromeHistoryClient* GetForProfile(Profile* profile);
+
+  static ChromeHistoryClientFactory* GetInstance();
+
+ private:
+  friend struct DefaultSingletonTraits<ChromeHistoryClientFactory>;
+
+  ChromeHistoryClientFactory();
+  virtual ~ChromeHistoryClientFactory();
+
+  // BrowserContextKeyedServiceFactory:
+  virtual KeyedService* BuildServiceInstanceFor(
+      content::BrowserContext* context) const OVERRIDE;
+  virtual content::BrowserContext* GetBrowserContextToUse(
+      content::BrowserContext* context) const OVERRIDE;
+  virtual bool ServiceIsNULLWhileTesting() const OVERRIDE;
+};
+
+#endif  // CHROME_BROWSER_HISTORY_CHROME_HISTORY_CLIENT_FACTORY_H_