Clarify thread safety of WebAudioSourceProvider interface.

third_party/WebKit/public/platform/WebAudioSourceProvider.h

 /*
  * Copyright (C) 2011, Google 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 19 matching lines @@
 namespace blink {
 
 class WebAudioSourceProviderClient;
 
 // Abstract interface for a pull-model client.
 class WebAudioSourceProvider {
  public:
   virtual ~WebAudioSourceProvider() {}
 
   // provideInput() gets called repeatedly to render time-slices of a continuous
-  // audio stream.
+  // audio stream. May be called from any thread.
   virtual void provideInput(const WebVector<float*>& audioData,
                             size_t numberOfFrames) = 0;
 
   // If a client is set, we call it back when the audio format is available.
+  // Must always be called from the same thread.

[Raymond Toy, 2016/11/29 19:17:12]

"same thread" as what?

[DaleCurtis, 2016/11/29 19:21:40]

I.e. if you're on t0 and call setClient(), all future calls must be issued on t0
as well. Is there language you would prefer? 

[Raymond Toy, 2016/11/29 19:23:50]

I think that's a perfect comment. "All future calls to setClient must be issued
from the same thread as the first call to setClient". Or something like that.

[DaleCurtis, 2016/11/29 19:30:22]

Done.

   virtual void setClient(WebAudioSourceProviderClient*) {}
 };
 
 }  // namespace blink
 
 #endif  // WebAudioSourceProvider_h