Made it possible to tell whether an extension is being installed or updated.

chrome/common/chrome_notification_types.h

 // Copyright 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_COMMON_CHROME_NOTIFICATION_TYPES_H_
 #define CHROME_COMMON_CHROME_NOTIFICATION_TYPES_H_
 
 #include "build/build_config.h"
 #include "content/public/browser/notification_types.h"
 
@@ skipping 479 matching lines @@
   // details are an Extension*, and the source is a Profile*.
   NOTIFICATION_EXTENSION_UPDATE_DISABLED,
 
   // Sent when an extension's permissions change. The details are an
   // UpdatedExtensionPermissionsInfo, and the source is a Profile.
   NOTIFICATION_EXTENSION_PERMISSIONS_UPDATED,
 
   // Sent when an extension install turns out to not be a theme.
   NOTIFICATION_NO_THEME_DETECTED,
 
-  // Sent when new extensions are installed. The details are an Extension, and
-  // the source is a Profile.
+  // Sent when new extensions are installed, or existing extensions are updated.
+  // The details are an InstalledExtensionInfo, and the source is a Profile.
   NOTIFICATION_EXTENSION_INSTALLED,
 
   // An error occured during extension install. The details are a string with
   // details about why the install failed.
   NOTIFICATION_EXTENSION_INSTALL_ERROR,
 
   // Sent when an extension install is not allowed, as indicated by
   // PendingExtensionInfo::ShouldAllowInstall. The details are an Extension,
   // and the source is a Profile.
   NOTIFICATION_EXTENSION_INSTALL_NOT_ALLOWED,
@@ skipping 716 matching lines @@
   // Note:-
   // Currently only Content and Chrome define and use notifications.
   // Custom notifications not belonging to Content and Chrome should start
   // from here.
   NOTIFICATION_CHROME_END,
 };
 
 }  // namespace chrome
 
 #endif  // CHROME_COMMON_CHROME_NOTIFICATION_TYPES_H_