Revert of Include event type name in tracing output for EventDispatcher (https://codereview.chromium.org/256873004/)

Reason for revert:
This appears to be causing crashes during touchpad scroll on Mac when about:tracing is active.

Original issue's description:
> Include event type name in tracing output for EventDispatcher
> 
> R=ojan
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172670

TBR=ojan@chromium.org,esprehn@chromium.org,rafaelw@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=368397

Review URL: https://codereview.chromium.org/255283004

git-svn-id: svn://svn.chromium.org/blink/trunk@172886 bbb929c8-8fbe-4397-9dbb-9b2b20218538