Fix autoupdate_EndToEndTest on veyron_rialto

base/callback_list.h

Index: base/callback_list.h
diff --git a/base/callback_list.h b/base/callback_list.h
index 7ab79dd8e1fcf79de5b76bc6e2586f49c7e3d974..c19c464c6fe6cc271512586cf4c74d318da8b182 100644
--- a/base/callback_list.h
+++ b/base/callback_list.h
@@ -120,6 +120,9 @@ class CallbackListBase {
     return callbacks_.empty();
   }
 
+  // Clears all the callbacks from this list.
+  void ClearAll() { callbacks_.clear(); }
+
  protected:
   // An iterator class that can be used to access the list of callbacks.
   class Iterator {