Prevent overlay play button from appearing during scrubbing

This CL adds a check in MediaControlsImpl::MaybeShow to only update the
overlay play button when we're not paused for scrubbing. This fixes a
bug where the overlay play button would appear on Android during
scrubbing.

Bug: 781721
Change-Id: If49ef77d2b4d9303d0fe147e51e622000751e8e3
Reviewed-on: https://chromium-review.googlesource.com/884761Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531892}

third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp

@@ -708,7 +708,7 @@ LayoutObject* MediaControlsImpl::ContainerLayoutObject() {
 void MediaControlsImpl::MaybeShow() {
   panel_->SetIsWanted(true);
   panel_->SetIsDisplayed(true);
-  if (overlay_play_button_)
+  if (overlay_play_button_ && !is_paused_for_scrubbing_)
     overlay_play_button_->UpdateDisplayType();
   // Only make the controls visible if they won't get hidden by OnTimeUpdate.
   if (MediaElement().paused() || !ShouldHideMediaControls())