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::IncrementInFlightEventCount() {
  ++in_flight_event_count_;
  if (!is_hidden_)
    StartHangMonitorTimeout(hung_renderer_delay_);
}

void RenderWidgetHostImpl::IncrementInFlightEventCount() {
  ++in_flight_event_count_;
  if (!is_hidden_)
    StartHangMonitorTimeout(hung_renderer_delay_);
}
