Unify and clean up system download notifications, add Mountain Lion support.

BUG=138962
TEST=as in bug


Review URL: https://chromiumcodereview.appspot.com/10827207

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@151195 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/supports_user_data.h b/base/supports_user_data.h
index 17899dd9..0a7c2dd 100644
--- a/base/supports_user_data.h
+++ b/base/supports_user_data.h
@@ -32,6 +32,7 @@
   // delete the object if it is changed or the object is destroyed.
   Data* GetUserData(const void* key) const;
   void SetUserData(const void* key, Data* data);
+  void RemoveUserData(const void* key);
 
  protected:
   virtual ~SupportsUserData();