Clarify thread safety of WebAudioSourceProvider interface.

third_party/WebKit/public/platform/WebAudioSourceProvider.h

Index: third_party/WebKit/public/platform/WebAudioSourceProvider.h
diff --git a/third_party/WebKit/public/platform/WebAudioSourceProvider.h b/third_party/WebKit/public/platform/WebAudioSourceProvider.h
index 115dd96ef37a64fb9b8d8c2b2914cf36617338b8..a901d8c2ed99f75190692478692fba50a25f0a56 100644
--- a/third_party/WebKit/public/platform/WebAudioSourceProvider.h
+++ b/third_party/WebKit/public/platform/WebAudioSourceProvider.h
@@ -37,11 +37,12 @@ class WebAudioSourceProvider {
   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*) {}
 };