Web Audio: when media playback requires a user gesture, apply rule to cross origin iframes.

third_party/WebKit/Source/modules/webaudio/AudioBufferSourceNode.cpp

Index: third_party/WebKit/Source/modules/webaudio/AudioBufferSourceNode.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/AudioBufferSourceNode.cpp b/third_party/WebKit/Source/modules/webaudio/AudioBufferSourceNode.cpp
index 24af794c3037d5967eea07a07b0568ca491d7ff4..4370ce56d8e103eeb43a1ed3e365afad5146a1f5 100644
--- a/third_party/WebKit/Source/modules/webaudio/AudioBufferSourceNode.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/AudioBufferSourceNode.cpp
@@ -448,7 +448,7 @@ void AudioBufferSourceHandler::startSource(double when, double grainOffset, doub
 {
     DCHECK(isMainThread());
 
-    context()->recordUserGestureState();
+    context()->startRenderingIfNeeded();

[Raymond Toy, 2016/09/07 16:13:19]

I don't think this is right.  When the context is created, startRendering() is
called immediately when the destination is created.  And if I understand what
you're trying to do, this might also interfere with any OfflineAudioContexts. 
These contexts shouldn't be require a gesture because they don't output any
audio.

[mlamouri (slow - plz ping), 2016/09/08 13:12:42]

When the AudioContext is created, it might not be rendering yet if there was no
user gesture. In this case, start() should resume automatically. 

Regarding offline audio context, I answered below: it's for compat with Safari
iOS. If both of you think there is really no reason to do this, let me know and
I can change that.

 
     if (playbackState() != UNSCHEDULED_STATE) {
         exceptionState.throwDOMException(