When autoplay of muted videos is disabled, record the reason why.

third_party/WebKit/Source/core/html/HTMLMediaElement.h

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 644 matching lines @@
     private:
         WebAudioSourceProvider* m_webAudioSourceProvider;
         Member<AudioClientImpl> m_client;
         Mutex provideInputLock;
     };
 
     AudioSourceProviderImpl m_audioSourceProvider;
 
     class AutoplayHelperClientImpl;
 
+    friend class AutoplayUmaHelper; // for isAutoplayAllowedPerSettings
     friend class Internals;
     friend class TrackDisplayUpdateScope;
     friend class AutoplayExperimentHelper;
     friend class MediaControlsTest;
 
     Member<AutoplayExperimentHelper::Client> m_autoplayHelperClient;
     Member<AutoplayExperimentHelper> m_autoplayHelper;
     Member<AutoplayUmaHelper> m_autoplayUmaHelper;
 
     WebRemotePlaybackClient* m_remotePlaybackClient;
 
     // class AutoplayVisibilityObserver;
     Member<ElementVisibilityObserver> m_autoplayVisibilityObserver;
 
     static URLRegistry* s_mediaStreamRegistry;
 };
 
 inline bool isHTMLMediaElement(const HTMLElement& element)
 {
     return isHTMLAudioElement(element) || isHTMLVideoElement(element);
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLMediaElement);
 
 } // namespace blink
 
 #endif // HTMLMediaElement_h