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The double-tap gesture on Aura (which causes zoom) does not respect the
touch-action filter as it should. i.e., double-tapping over a region
with touch-action: none should prevent zooming.

This is caused by IsGestureEvent() returning false for the
TAP_UNCONFIRMED event. IsGestureEvent is used in EventHandler::OnEvent
to determine whether to pass the event to OnGestureEvent and meant that
the TAP_UNCONFIRMED gesture would get dropped at this point.

The reason this was working on Android was that Android's
GestureProivderClient is RenderWidgetHostViewAndroid. When
FilteredGestureProvider forwards the gesture it passes it straight back
to the RWHVA which doesn't go through the IsGestureEvent check mentioned
above.

On Aura, the GestureProviderClient is GestureProviderAura which passes
the forwarded gesture back through WindowEventDispatch before finding
the RenderWidgetHostViewAura. The WindowEventDispatch call chain is
where we accidentally filtered the TAP_UNCONFIRMED gesture because of
!IsGestureEvent. This means the TouchActionFilter never saw this
gesture, which it needs to determine whether to filter the subsequent
double-tap gesture.

Bug: 865090
Change-Id: I5f8932dcf8b33ec132fa946864a462610cc8413b
Reviewed-on: https://chromium-review.googlesource.com/1213881Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590173}