Make EventListenerMap::ContainsCapturing after a failed search of the listener vector.

There can never be two separate map entries with different event names, so
continuing to search is pointless.

Change-Id: I4a91e17b99bfa723b965349e564613ab64bfc69a
Reviewed-on: https://chromium-review.googlesource.com/581428Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488739}

third_party/WebKit/Source/core/events/EventListenerMap.cpp

@@ -72,6 +72,7 @@ bool EventListenerMap::ContainsCapturing(const AtomicString& event_type) const {
         if (event_listener.Capture())
           return true;
       }
+      return false;
     }
   }
   return false;