Redraw media volume slider when it is moving

third_party/WebKit/Source/core/html/shadow/MediaControls.cpp

 /*
  * Copyright (C) 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 788 matching lines @@
   m_volumeSlider->setVolume(mediaElement().muted() ? 0
                                                    : mediaElement().volume());
 
   // Update visibility of volume controls.
   // TODO(mlamouri): it should not be part of the volumechange handling because
   // it is using audio availability as input.
   BatchedControlUpdate batch(this);
   m_volumeSlider->setIsWanted(mediaElement().hasAudio() &&
                               !preferHiddenVolumeControls(document()));
   m_muteButton->setIsWanted(mediaElement().hasAudio());
+  invalidate(m_muteButton);

[CJ, 2017/03/28 14:58:38]

Is this necessary?

+  invalidate(m_volumeSlider);
 }
 
 void MediaControls::onFocusIn() {
   if (!mediaElement().shouldShowControls())
     return;
 
   show();
   resetHideMediaControlsTimer();
 }
 
@@ skipping 281 matching lines @@
   visitor->trace(m_overflowList);
   visitor->trace(m_castButton);
   visitor->trace(m_overlayCastButton);
   visitor->trace(m_mediaEventListener);
   visitor->trace(m_windowEventListener);
   visitor->trace(m_orientationLockDelegate);
   HTMLDivElement::trace(visitor);
 }
 
 }  // namespace blink