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

chrome/browser/favicon/favicon_service_factory.h

 // Copyright (c) 2012 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_FAVICON_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_FAVICON_FAVICON_SERVICE_FACTORY_H_
 
 #include "base/memory/singleton.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 FaviconService;
 class Profile;
 
 // Singleton that owns all FaviconService and associates them with
 // Profiles.
 class FaviconServiceFactory : public BrowserContextKeyedServiceFactory {
  public:
-  // |access| defines what the caller plans to do with the service. See
+  // |sat| defines what the caller plans to do with the service. See
   // the ServiceAccessType definition in profile.h.
   static FaviconService* GetForProfile(Profile* profile, ServiceAccessType sat);
 
   static FaviconServiceFactory* GetInstance();
 
  private:
   friend struct DefaultSingletonTraits<FaviconServiceFactory>;
 
   FaviconServiceFactory();
   ~FaviconServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const override;
   bool ServiceIsNULLWhileTesting() const override;
 
   DISALLOW_COPY_AND_ASSIGN(FaviconServiceFactory);
 };
 
 #endif  // CHROME_BROWSER_FAVICON_FAVICON_SERVICE_FACTORY_H_