Revert 251382 "event-rewrite: Clean up how events are rewritten."

> event-rewrite: Clean up how events are rewritten.
> 
> Notable changes:
>  * Make the EventRewriter a MessagePumpObserver. This is necessary to make sure
>    that the event-rewrite happens before the event is dispatched.
>  * Move the EventRewriter in chrome/browser/chromeos (and in chromeos namespace),
>    since it does nothing on other platforms.
>  * Get rid of the event-rewrite code from ash, since it just adds an extra layer
>    of abstraction for no added value.
> 
> BUG=343639
> R=derat@chromium.org, sky@chromium.org, stevenjb@chromium.org
> 
> Review URL: https://codereview.chromium.org/165463002

This was causing the following check failure

[3943:3943:0214/135331:FATAL:event_rewriter.cc(858)] Check failed:
xievent->evtype == XI_ButtonPress || xievent->evtype == XI_ButtonRelease. 
Aborted (core dumped)

TBR=sadrul@chromium.org

Review URL: https://codereview.chromium.org/167273003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251433 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251433