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

chrome/browser/extensions/crx_installer.h

Index: chrome/browser/extensions/crx_installer.h
diff --git a/chrome/browser/extensions/crx_installer.h b/chrome/browser/extensions/crx_installer.h
index 90ad00134ae94916ac6c0eaa4f5811fb1a407d1d..4d9cfb8775dd7664be9e6322978d65ace71de803 100644
--- a/chrome/browser/extensions/crx_installer.h
+++ b/chrome/browser/extensions/crx_installer.h
@@ -247,8 +247,10 @@ class CrxInstaller
   // 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_;
@@ -393,6 +395,9 @@ class CrxInstaller
   // 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);
 };