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

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

 /*
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  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
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@@ skipping 430 matching lines @@
 
 void AudioBufferSourceHandler::start(double when, double grainOffset, double grainDuration, ExceptionState& exceptionState)
 {
     startSource(when, grainOffset, grainDuration, true, exceptionState);
 }
 
 void AudioBufferSourceHandler::startSource(double when, double grainOffset, double grainDuration, bool isDurationGiven, ExceptionState& exceptionState)
 {
     DCHECK(isMainThread());
 
-    context()->recordUserGestureState();
+    context()->startRenderingIfNeeded();

[Raymond Toy, 2016/09/08 20:03:33]

If we don't have the gesture, we don't want to start.  In that case, we should
just return early from here.

But this depends on what you expect to happen.  In this current version, if we
don't have the gesture, we don't "render", but we do everything else we would
normally do.  So, if, say in a second, we do get the gesture, the buffer will
start playing, skipping over the first second of audio.

Is that the intent?  If so, we'll have to think of something else.

[mlamouri (slow - plz ping), 2016/09/12 17:26:29]

This is the intended behaviour, it matches
https://github.com/WebKit/webkit/blob/d61d8c1359eab56e2337c50da8f9c168783e722...

 
     if (playbackState() != UNSCHEDULED_STATE) {
         exceptionState.throwDOMException(
             InvalidStateError,
             "cannot call start more than once.");
         return;
     }
 
     if (when < 0) {
         exceptionState.throwDOMException(
@@ skipping 228 matching lines @@
 {
     audioBufferSourceHandler().start(when, grainOffset, exceptionState);
 }
 
 void AudioBufferSourceNode::start(double when, double grainOffset, double grainDuration, ExceptionState& exceptionState)
 {
     audioBufferSourceHandler().start(when, grainOffset, grainDuration, exceptionState);
 }
 
 } // namespace blink