[Fallback Icons] Refactor FallbackIconService to be a BrowserContext-level singleton

chrome/browser/favicon/fallback_icon_service_factory.h

+// 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.
+
+#ifndef CHROME_BROWSER_FAVICON_FALLBACK_ICON_SERVICE_FACTORY_H_
+#define CHROME_BROWSER_FAVICON_FALLBACK_ICON_SERVICE_FACTORY_H_
+
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+#include "components/keyed_service/core/service_access_type.h"
+
+template <typename T> struct DefaultSingletonTraits;
+
+class FallbackIconService;
+class Profile;
+
+// Singleton that owns all FallbackIconService and associates them with
+// Profiles.
+class FallbackIconServiceFactory : public BrowserContextKeyedServiceFactory {
+ public:
+  // |access| defines what the caller plans to do with the service. See
+  // the ServiceAccessType definition in profile.h.
+  static FallbackIconService* GetForProfile(
+      Profile* profile, ServiceAccessType sat);
+
+  static FallbackIconServiceFactory* GetInstance();
+
+ private:
+  friend struct DefaultSingletonTraits<FallbackIconServiceFactory>;
+
+  FallbackIconServiceFactory();
+  ~FallbackIconServiceFactory() override;
+
+  // BrowserContextKeyedServiceFactory:
+  KeyedService* BuildServiceInstanceFor(
+      content::BrowserContext* profile) const override;
+  bool ServiceIsNULLWhileTesting() const override;
+
+  DISALLOW_COPY_AND_ASSIGN(FallbackIconServiceFactory);
+};
+
+#endif  // CHROME_BROWSER_FAVICON_FALLBACK_ICON_SERVICE_FACTORY_H_