Introduce HostID and de-couple Extensions from "script injection System" [browser side]

chrome/browser/extensions/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 CHROME_BROWSER_EXTENSIONS_DECLARATIVE_USER_SCRIPT_MANAGER_H_
 #define CHROME_BROWSER_EXTENSIONS_DECLARATIVE_USER_SCRIPT_MANAGER_H_
 
 #include <map>
 
 #include "base/macros.h"
 #include "base/memory/linked_ptr.h"
+#include "base/scoped_observer.h"
+#include "extensions/browser/extension_registry_observer.h"
+#include "extensions/common/host_id.h"
 
 class Profile;
 
 namespace extensions {
 class DeclarativeUserScriptMaster;
 
 // Manages a set of DeclarativeUserScriptMaster objects for script injections.
-class DeclarativeUserScriptManager {
+class DeclarativeUserScriptManager : public ExtensionRegistryObserver {
  public:
   explicit DeclarativeUserScriptManager(Profile* profile);
-  ~DeclarativeUserScriptManager();
+  ~DeclarativeUserScriptManager() override;
 
-  // Get the user script master for declarative scripts; if one does not exist,
-  // a new object will be created.
+  // 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 std::string& id);
+      const HostID& host_id);
 
  private:
   using UserScriptMasterMap =
-      std::map<std::string, linked_ptr<DeclarativeUserScriptMaster>>;
+      std::map<HostID, linked_ptr<DeclarativeUserScriptMaster>>;
 
-  // A map of DeclarativeUserScriptMasters for ids; each master is lazily
-  // initialized.
+  // ExtensionRegistryObserver:
+  void OnExtensionUnloaded(content::BrowserContext* browser_context,
+                           const Extension* extension,
+                           UnloadedExtensionInfo::Reason reason) override;
+
+  // Creates a DeclarativeUserScriptMaster object.
+  DeclarativeUserScriptMaster* CreateDeclarativeUserScriptMaster(
+      const HostID& host_id);
+
+  // A map of DeclarativeUserScriptMasters for each host; each master
+  // is lazily initialized.
   UserScriptMasterMap declarative_user_script_masters_;
 
   Profile* profile_;
 
+  ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
+      extension_registry_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(DeclarativeUserScriptManager);
 };
 
-}  // extensions
+}  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_DECLARATIVE_USER_SCRIPT_MANAGER_H_