Extract DeclarativeUserScriptManager from ExtensionSystem.

extensions/browser/declarative_user_script_manager.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 EXTENSIONS_BROWSER_DECLARATIVE_USER_SCRIPT_MANAGER_H_
 #define EXTENSIONS_BROWSER_DECLARATIVE_USER_SCRIPT_MANAGER_H_
 
 #include <map>
 
 #include "base/macros.h"
 #include "base/memory/linked_ptr.h"
 #include "base/scoped_observer.h"
+#include "components/keyed_service/core/keyed_service.h"
 #include "extensions/browser/extension_registry_observer.h"
 #include "extensions/common/host_id.h"
 
 namespace content {
 class BrowserContext;
 }
 
 namespace extensions {
 class DeclarativeUserScriptMaster;
 
 // Manages a set of DeclarativeUserScriptMaster objects for script injections.
-class DeclarativeUserScriptManager : public ExtensionRegistryObserver {
+class DeclarativeUserScriptManager : public KeyedService,
+                                     public ExtensionRegistryObserver {
  public:
   explicit DeclarativeUserScriptManager(
       content::BrowserContext* browser_context);
   ~DeclarativeUserScriptManager() override;
 
+  // Convenience method to return the DeclarativeUserScriptManager for a given
+  // |context|.
+  static DeclarativeUserScriptManager* Get(content::BrowserContext* context);
+
   // Gets the user script master for declarative scripts by the given
   // HostID; if one does not exist, a new object will be created.
   DeclarativeUserScriptMaster* GetDeclarativeUserScriptMasterByID(
       const HostID& host_id);
 
  private:
   using UserScriptMasterMap =
       std::map<HostID, linked_ptr<DeclarativeUserScriptMaster>>;
 
   // ExtensionRegistryObserver:
@@ skipping 13 matching lines @@
 
   ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
       extension_registry_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(DeclarativeUserScriptManager);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_DECLARATIVE_USER_SCRIPT_MANAGER_H_