Add support to Google Update wrappers for the "automatic updates only" group policy setting.

chrome/browser/google/google_update_win.h

Index: chrome/browser/google/google_update_win.h
===================================================================
--- chrome/browser/google/google_update_win.h	(revision 205261)
+++ chrome/browser/google/google_update_win.h	(working copy)
@@ -56,8 +56,12 @@
   // An error occurred while upgrading (or while checking for update).
   // Check the Google Update log in %TEMP% for more details.
   GOOGLE_UPDATE_ERROR_UPDATING,
-  // Updates can not be downloaded because the administrator has disabled them.
+  // Updates can not be downloaded because the administrator has disabled all
+  // types of updating.
   GOOGLE_UPDATE_DISABLED_BY_POLICY,
+  // Updates can not be downloaded because the administrator has disabled
+  // manual (on-demand) updates.  Automatic background updates are allowed.
+  GOOGLE_UPDATE_DISABLED_BY_POLICY_AUTO_ONLY,
 };
 
 // The GoogleUpdateStatusListener interface is used by components to receive