Disable an extension when it is upgraded to a version that requires more

chrome/common/extensions/extension.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_COMMON_EXTENSIONS_EXTENSION_H_
 #define CHROME_COMMON_EXTENSIONS_EXTENSION_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 15 matching lines @@
   enum Location {
     INVALID,
     INTERNAL,           // A crx file from the internal Extensions directory.
     EXTERNAL_PREF,      // A crx file from an external directory (via prefs).
     EXTERNAL_REGISTRY,  // A crx file from an external directory (via eg the
                         // registry on Windows).
     LOAD                // --load-extension.
   };
 
   enum State {
-    DISABLED,
+    DISABLED = 0,
     ENABLED,
     KILLBIT,  // Don't install/upgrade (applies to external extensions only).
+
+    NUM_STATES
   };
 
   enum InstallType {
     INSTALL_ERROR,
     DOWNGRADE,
     REINSTALL,
     UPGRADE,
     NEW_INSTALL
   };
 
@@ skipping 291 matching lines @@
 
   // True if the background page is ready.
   bool background_page_ready_;
 
   FRIEND_TEST(ExtensionTest, LoadPageActionHelper);
 
   DISALLOW_COPY_AND_ASSIGN(Extension);
 };
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_H_