[Picture in Picture] Call parent function in OnGestureEvent.

Change-Id: I854654be22abd217c3f8ed557bc3fb9118c557c6
Reviewed-on: https://chromium-review.googlesource.com/1192326Reviewed-by: CJ DiMeglio <lethalantidote@chromium.org>
Commit-Queue: apacible <apacible@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586820}

chrome/browser/ui/views/overlay/overlay_window_views.cc

@@ -643,6 +643,8 @@ void OverlayWindowViews::OnGestureEvent(ui::GestureEvent* event) {
     TogglePlayPause();
     event->SetHandled();
   }
+
+  views::Widget::OnGestureEvent(event);
 }
 
 void OverlayWindowViews::ButtonPressed(views::Button* sender,