Use media controls play button's width rather than hard-coded 48px.

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 683 matching lines @@
         m_timeline.get(),
         m_currentTimeDisplay.get(),
         m_volumeSlider.get(),
         m_castButton.get(),
         m_muteButton.get(),
         m_durationDisplay.get(),
     };
 
     int usedWidth = 0;
     bool droppedCastButton = false;
-    // Assume that all controls require 48px.  Ideally, we could get this from
-    // the computed style, but that requires the controls to be shown.
-    const int minimumWidth = 48;
+
+    // Assume that all controls require 48px, unless we can get the computed
+    // style for the play button.  Since the play button is always shown, it
+    // should be available the first time we're called after layout.  This will
+    // also be the first time we have m_panelWidth!=0, so it won't matter if
+    // we get this wrong before that.
+    int minimumWidth = (m_playButton->layoutObject() && m_playButton->layoutObject()->style())
+        ? m_playButton->layoutObject()->style()->width().pixels()
+        : 48;

[mlamouri (slow - plz ping), 2016/05/09 12:41:39]

`minimumWidth` is being used by all elements in `elements`. They will have a
different size than the play button. Is there a reason why we use the play
button size for those?

 
     // Special-case the play button; it always fits.
     if (m_playButton->isWanted()) {
         m_playButton->setDoesFit(true);
         usedWidth += minimumWidth;
     }
 
     if (!m_panelWidth) {
         // No layout yet -- hide everything, then make them show up later.
         // This prevents the wrong controls from being shown briefly
@@ skipping 74 matching lines @@
     visitor->trace(m_fullScreenButton);
     visitor->trace(m_durationDisplay);
     visitor->trace(m_enclosure);
     visitor->trace(m_textTrackList);
     visitor->trace(m_castButton);
     visitor->trace(m_overlayCastButton);
     HTMLDivElement::trace(visitor);
 }
 
 } // namespace blink