Get rid of the extension's "Current Version" file.

chrome/browser/extensions/crx_installer.h

 // Copyright (c) 2009 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/file_path.h"
@@ skipping 120 matching lines @@
   // The message loop to use for file IO.
   MessageLoop* file_loop_;
 
   // The message loop the UI is running on.
   MessageLoop* ui_loop_;
 
   // The extension we're installing. We own this and either pass it off to
   // ExtensionsService on success, or delete it on failure.
   scoped_ptr<Extension> extension_;
 
+  // If non-empty, contains the current version of the extension we're
+  // installing (for upgrades).
+  std::string current_version_;
+
   // The icon we will display in the installation UI, if any.
   scoped_ptr<SkBitmap> install_icon_;
 
   // The temp directory extension resources were unpacked to. We own this and
   // must delete it when we are done with it.
   FilePath temp_dir_;
 
   // The frontend we will report results back to.
   scoped_refptr<ExtensionsService> frontend_;
 
   // The client we will work with to do the installation. This can be NULL, in
   // which case the install is silent.
   scoped_ptr<ExtensionInstallUI> client_;
 
   // The root of the unpacked extension directory. This is a subdirectory of
   // temp_dir_, so we don't have to delete it explicitly.
   FilePath unpacked_extension_root_;
 
   // The unpacker we will use to unpack the extension.
   SandboxedExtensionUnpacker* unpacker_;
 
   DISALLOW_COPY_AND_ASSIGN(CrxInstaller);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_CRX_INSTALLER_H_