Update extensions with Drag-and-Drop in extension settings page.

chrome/browser/extensions/crx_installer.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_CRX_INSTALLER_H_
 #define CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 229 matching lines @@
   void ReportFailureFromUIThread(const CrxInstallerError& error);
   void ReportSuccessFromFileThread();
   void ReportSuccessFromUIThread();
   void HandleIsBlacklistedResponse(const base::Closure& on_success,
                                    bool success);
   void NotifyCrxInstallComplete(bool success);
 
   // Deletes temporary directory and crx file if needed.
   void CleanupTempFiles();
 
-  // Creates sequenced task runner for extension install file I/O operations.
-  scoped_refptr<base::SequencedTaskRunner> CreateSequencedTaskRunner();
+  // Checks whether a previous version of the given |extension| is already
+  // installed. If exists, find out whether a prompt should be shown at the
+  // time of updating the |extension|.
+  void CheckExtensionExistsAlready(const Extension* extension);
 
   // The file we're installing.
   base::FilePath source_file_;
 
   // The URL the file was downloaded from.
   GURL download_url_;
 
   // The directory extensions are installed to.
   base::FilePath install_directory_;
 
@@ skipping 124 matching lines @@
   bool has_requirement_errors_;
 
   bool install_wait_for_idle_;
 
   // Sequenced task runner where file I/O operations will be performed.
   scoped_refptr<base::SequencedTaskRunner> installer_task_runner_;
 
   // Used to show the install dialog.
   ExtensionInstallPrompt::ShowDialogCallback show_dialog_callback_;
 
+  // Whether to show update prompt.
+  bool show_update_prompt_;
+
   DISALLOW_COPY_AND_ASSIGN(CrxInstaller);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_