Supporting a playbackTime attribute on AudioprocessingEvent.

Source/modules/webaudio/ScriptProcessorNode.cpp

Index: Source/modules/webaudio/ScriptProcessorNode.cpp
diff --git a/Source/modules/webaudio/ScriptProcessorNode.cpp b/Source/modules/webaudio/ScriptProcessorNode.cpp
index 79c446c96f432d7f6cfed6d71feae697b7e15993..45bf3a74226b8e3bb4a8d7f328c8a530a99806e9 100644
--- a/Source/modules/webaudio/ScriptProcessorNode.cpp
+++ b/Source/modules/webaudio/ScriptProcessorNode.cpp
@@ -265,8 +265,12 @@ void ScriptProcessorNode::fireProcessEvent()
         // Let the audio thread know we've gotten to the point where it's OK for it to make another request.
         m_isRequestOutstanding = false;
 
+        // Calculate a playbackTime with the buffersize which needs to be processed each time onaudioprocess is called.
+        // The outputBuffer being passed to JS will be played after exhuasting previous outputBuffer by double-buffering.
+        double playbackTime = (context()->currentSampleFrame() + m_bufferSize) / static_cast<double>(context()->sampleRate());
+
         // Call the JavaScript event handler which will do the audio processing.
-        dispatchEvent(AudioProcessingEvent::create(inputBuffer, outputBuffer));
+        dispatchEvent(AudioProcessingEvent::create(inputBuffer, outputBuffer, playbackTime));
     }
 }