Update autoplay settings when moving media elements between documents

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

 /*
  * 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:
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@@ skipping 469 matching lines @@
     // doesn't get dispatched during the object destruction.
     // See Document::isDelayingLoadEvent().
     // Also see http://crbug.com/275223 for more details.
     clearMediaPlayerAndAudioSourceProviderClientWithoutLocking();
 }
 
 void HTMLMediaElement::didMoveToNewDocument(Document& oldDocument)
 {
     DVLOG(MEDIA_LOG_LEVEL) << "didMoveToNewDocument(" << (void*)this << ")";
 
+    // If any experiment is enabled, then we want to enable a user gesture by
+    // default, otherwise the experiment does nothing.
+    if ((document().settings() && document().settings()->mediaPlaybackRequiresUserGesture())
+        || m_autoplayHelper->isExperimentEnabled()) {

[mlamouri (slow - plz ping), 2016/06/07 15:40:28]

I think you should do something like:
```
bool oldDocumentRequiresUserGesture = <what you did but for the old document>
bool newDocumentRequiresUserGesture = <what you did>
if (newDocumentRequiresUserGesture && !oldDocumentRequiresUserGesture)
    m_lockedPendingUserGesture = true;
```

I'm afraid what you wrote here would re-set to true the lock after the document
move regardless of the context.

[Zhiqiang Zhang (Slow), 2016/06/07 17:02:40]

Done.

+        m_lockedPendingUserGesture = true;
+    }
+
     if (m_shouldDelayLoadEvent) {
         document().incrementLoadEventDelayCount();
         // Note: Keeping the load event delay count increment on oldDocument that was added
         // when m_shouldDelayLoadEvent was set so that destruction of m_webMediaPlayer can not
         // cause load event dispatching in oldDocument.
     } else {
         // Incrementing the load event delay count so that destruction of m_webMediaPlayer can not
         // cause load event dispatching in oldDocument.
         oldDocument.incrementLoadEventDelayCount();
     }
@@ skipping 3381 matching lines @@
 
 IntRect HTMLMediaElement::AutoplayHelperClientImpl::absoluteBoundingBoxRect() const
 {
     IntRect result;
     if (LayoutObject* object = m_element->layoutObject())
         result = object->absoluteBoundingBoxRect();
     return result;
 }
 
 } // namespace blink