events: Change gesture-event handler in EventHandler to not return any values.

events: Change gesture-event handler in EventHandler to not return any values.

The EventHandler overriddes should mark the event as having been processed
(Event::SetHandled) when the event triggered an action, or stop the propagation
of the event (Event::StopPropagation) as appropriate (when the handler destroyed
the event-target, for example).

BUG=163618
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=170890

[Ben Goodger (Google), 2012-12-04 03:12:06]

lgtm