Force a flush of drawing to the widget when a dialog is shown.

BUG=823353
TEST=as in bug

Change-Id: I5da777068fc29c5638ef02d50e59d5d7b2729260
Reviewed-on: https://chromium-review.googlesource.com/971661
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544518}
void RenderWidgetHostImpl::OnGestureEventAck(
    const GestureEventWithLatencyInfo& event,
    InputEventAckSource ack_source,
    InputEventAckState ack_result) {
  latency_tracker_.OnInputEventAck(event.event, &event.latency, ack_result);
  for (auto& input_event_observer : input_event_observers_)
    input_event_observer.OnInputEventAck(ack_source, ack_result, event.event);

  if (touch_emulator_)
    touch_emulator_->OnGestureEventAck(event.event);

  if (view_)
    view_->GestureEventAck(event.event, ack_result);
}

void RenderWidgetHostImpl::OnGestureEventAck(
    const GestureEventWithLatencyInfo& event,
    InputEventAckSource ack_source,
    InputEventAckState ack_result) {
  latency_tracker_.OnInputEventAck(event.event, &event.latency, ack_result);
  for (auto& input_event_observer : input_event_observers_)
    input_event_observer.OnInputEventAck(ack_source, ack_result, event.event);

  if (touch_emulator_)
    touch_emulator_->OnGestureEventAck(event.event);

  if (view_)
    view_->GestureEventAck(event.event, ack_result);
}
