[Extensions Page] Add a listener on extension list for "hasExtensions" changing

chrome/browser/extensions/api/developer_private/developer_private_api.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_EXTENSIONS_API_DEVELOPER_PRIVATE_DEVELOPER_PRIVATE_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DEVELOPER_PRIVATE_DEVELOPER_PRIVATE_API_H_
 
 #include <set>
 
 #include "base/files/file.h"
@@ skipping 65 matching lines @@
   void AddExtensionId(const std::string& extension_id);
   void RemoveExtensionId(const std::string& extension_id);
 
  private:
   // ExtensionRegistryObserver:
   void OnExtensionLoaded(content::BrowserContext* browser_context,
                          const Extension* extension) override;
   void OnExtensionUnloaded(content::BrowserContext* browser_context,
                            const Extension* extension,
                            UnloadedExtensionInfo::Reason reason) override;
-  void OnExtensionWillBeInstalled(content::BrowserContext* browser_context,
-                                  const Extension* extension,
-                                  bool is_update,
-                                  bool from_ephemeral,
-                                  const std::string& old_name) override;
+  void OnExtensionInstalled(content::BrowserContext* browser_context,
+                            const Extension* extension,
+                            bool is_update) override;
   void OnExtensionUninstalled(content::BrowserContext* browser_context,
                               const Extension* extension,
                               extensions::UninstallReason reason) override;
 
   // ErrorConsole::Observer:
   void OnErrorAdded(const ExtensionError* error) override;
 
   // ProcessManagerObserver:
   void OnExtensionFrameRegistered(
       const std::string& extension_id,
@@ skipping 427 matching lines @@
  protected:
   ~DeveloperPrivateShowPathFunction() override;
   ResponseAction Run() override;
 };
 
 }  // namespace api
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DEVELOPER_PRIVATE_DEVELOPER_PRIVATE_API_H_