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

chrome/browser/extensions/extension_prefs.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_EXTENSION_PREFS_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_PREFS_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 31 matching lines @@
   // Called when an extension is uninstalled, so that prefs get cleaned up.
   void OnExtensionUninstalled(const Extension* extension,
                               bool external_uninstall);
 
   // Returns the state (enabled/disabled) of the given extension.
   Extension::State GetExtensionState(const std::string& extension_id);
 
   // Called to change the extension's state when it is enabled/disabled.
   void SetExtensionState(Extension* extension, Extension::State);
 
+  // Returns the version string for the currently installed extension, or
+  // the empty string if not found.
+  std::string GetVersionString(const std::string& extension_id);
+
+  // Ensure old extensions have fully up-to-date prefs values.
+  void MigrateToPrefs(Extension* extension);
+
   // Returns base extensions install directory.
   const FilePath& install_directory() const { return install_directory_; }
 
   // Updates the prefs based on the blacklist.
   void UpdateBlacklist(const std::set<std::string>& blacklist_set);
 
   // Based on extension id, checks prefs to see if it is blacklisted.
   bool IsExtensionBlacklisted(const std::string& id);
 
  private:
@@ skipping 37 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(ExtensionPrefs);
 };
 
 // A helper class that has a list of the currently installed extensions
 // and can iterate over them to a provided callback.
 class InstalledExtensions {
  public:
   explicit InstalledExtensions(ExtensionPrefs* prefs);
   ~InstalledExtensions();
 
-  typedef Callback3<const std::string&,
+  typedef Callback4<DictionaryValue*,
+                    const std::string&,
                     const FilePath&,
                     Extension::Location>::Type Callback;
 
   // Runs |callback| for each installed extension with the path to the
   // version directory and the location. Blacklisted extensions won't trigger
-  // the callback.
+  // the callback. Ownership of |callback| is transferred to callee.
   void VisitInstalledExtensions(Callback *callback);
 
-  // Same as above, but only for the given extension.
-  void VisitInstalledExtension(const std::string& extension_id,
-                               Callback *callback);
-
  private:
   // A copy of the extensions pref dictionary so that this can be passed
   // around without a dependency on prefs.
   scoped_ptr<DictionaryValue> extension_data_;
 
   DISALLOW_COPY_AND_ASSIGN(InstalledExtensions);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_PREFS_H_