Merge r8050 - When a function handling an event doesn't return a value, it le...

Merge r8050 - When a function handling an event doesn't return a value, it leaves
the "event" object on the global context. This namespace pollution
was causing some functionality that was trying to detect if we were
in an event, such as popup blocking, to go wrong.

BUG=6367
Review URL: http://codereview.chromium.org/18013
TBR=erg@google.com
RNOTE=Fix to prevent us from incorrectly blocking popups



Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=8516