Adding an experimental flag to block autoplay with sound in cross-origin iframes

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:
  * 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 264 matching lines @@
     case WebMediaPlayer::PreloadMetaData:
       return "metadata";
     case WebMediaPlayer::PreloadAuto:
       return "auto";
   }
 
   NOTREACHED();
   return String();
 }
 
+bool isCrossOrigin(Document& document) {
+  const LocalFrame* frame = document.frame();
+  return frame && frame->isCrossOriginSubframe();
+}
+
 }  // anonymous namespace
 
 class HTMLMediaElement::AutoplayHelperClientImpl
     : public AutoplayExperimentHelper::Client {
  public:
   static AutoplayHelperClientImpl* create(HTMLMediaElement* element) {
     return new AutoplayHelperClientImpl(element);
   }
 
   virtual ~AutoplayHelperClientImpl();
@@ skipping 169 matching lines @@
       m_remotePlaybackClient(nullptr),
       m_autoplayVisibilityObserver(nullptr) {
   ThreadState::current()->registerPreFinalizer(this);
 
   BLINK_MEDIA_LOG << "HTMLMediaElement(" << (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()) ||
+      (document.settings() && isCrossOrigin(document) &&

[whywhat, 2016/11/16 17:37:17]

is it this that you don't like? you could've had a helper function that takes a
document and returns true if it requires user gesture for 

bool HTMLMediaElement::documentRequiresUserGesture(const Document& document) {
  // might be a good time to remove this? :)
  if (m_autoplayHelper->isExperimentEnabled()) return true;

  if (!document.settings()) return false;

  return document.settings()->mediaPlaybackRequiresUserGesture() ||
      (document.settings()->mediaPlaybackinCORequiresUserGesture() &&
isCrossOrigin(document));
}

[Zhiqiang Zhang (Slow), 2016/11/16 18:11:40]

Already merged them into a helper function in my local patch :)

I'm more concerned about the plumbing, i.e. plumbing another boolean flag from
chrome://flags to WebKit Settings. It lacks some flexibility in case if we have
more variations for autoplay. Also, currently we are having
"MediaPlaybackRequiresUserGesture" and
"MediaPlaybackInCrossOriginIframesRequiresUserGesture" side-by-side in Blink
neglect of which platform we are on, while they do not co-exist in content/
because of the #ifdef macros. This would bring some confusion.

So what I'm thinking is to make "MediaPlaybackRequiresUserGesture" available to
all platforms, and have an optional string flag indicating the autoplay
variations. WDYT?

+       document.settings()
+           ->mediaPlaybackInCrossOriginIframesRequiresUserGesture()) ||
       m_autoplayHelper->isExperimentEnabled()) {
     m_lockedPendingUserGesture = true;
   }
 
   LocalFrame* frame = document.frame();
   if (frame) {
     m_remotePlaybackClient =
         frame->loader().client()->createWebRemotePlaybackClient(*this);
   }
 
@@ skipping 28 matching lines @@
 
 void HTMLMediaElement::didMoveToNewDocument(Document& oldDocument) {
   BLINK_MEDIA_LOG << "didMoveToNewDocument(" << (void*)this << ")";
 
   m_autoplayUmaHelper->didMoveToNewDocument(oldDocument);
   // If any experiment is enabled, then we want to enable a user gesture by
   // default, otherwise the experiment does nothing.
   bool oldDocumentRequiresUserGesture =
       (oldDocument.settings() &&
        oldDocument.settings()->mediaPlaybackRequiresUserGesture()) ||
+      (oldDocument.settings() && isCrossOrigin(oldDocument) &&
+       oldDocument.settings()
+           ->mediaPlaybackInCrossOriginIframesRequiresUserGesture()) ||
       m_autoplayHelper->isExperimentEnabled();
   bool newDocumentRequiresUserGesture =
       (document().settings() &&
        document().settings()->mediaPlaybackRequiresUserGesture()) ||
+      (document().settings() && isCrossOrigin(oldDocument) &&
+       document()
+           .settings()
+           ->mediaPlaybackInCrossOriginIframesRequiresUserGesture()) ||
       m_autoplayHelper->isExperimentEnabled();
   if (newDocumentRequiresUserGesture && !oldDocumentRequiresUserGesture) {
     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.
@@ skipping 3653 matching lines @@
 
 IntRect HTMLMediaElement::AutoplayHelperClientImpl::absoluteBoundingBoxRect()
     const {
   IntRect result;
   if (LayoutObject* object = m_element->layoutObject())
     result = object->absoluteBoundingBoxRect();
   return result;
 }
 
 }  // namespace blink