Access current frame counter carefully and remove m_cachedSampleFrame.

Source/modules/webaudio/AudioContext.h

Index: Source/modules/webaudio/AudioContext.h
diff --git a/Source/modules/webaudio/AudioContext.h b/Source/modules/webaudio/AudioContext.h
index 9ea7dd20da78526b65d5dd0672f0bbab69918f50..bfb33051c35606bc57ea36da3a23eabdf796e336 100644
--- a/Source/modules/webaudio/AudioContext.h
+++ b/Source/modules/webaudio/AudioContext.h
@@ -108,12 +108,15 @@ public:
 
     AudioDestinationNode* destination() { return m_destinationNode.get(); }
 
-    // currentSampleFrame() and currentTime() can be called from both the main
-    // thread and the audio thread. Note that, however, they return the cached
-    // value instead of actual current ones when they are accessed from the main
-    // thread. See: crbug.com/431874
-    size_t currentSampleFrame() const;
-    double currentTime() const;
+    size_t currentSampleFrame() const
+    {
+        return m_destinationNode ? m_destinationNode->audioDestinationHandler().currentSampleFrame() : 0;

[Ken Russell (switch to Gerrit), 2015/05/21 20:45:16]

Is it safe to access the destination node's AudioDestinationHandler from the
main thread? The previous code only accessed it from the audio thread.

[Raymond Toy, 2015/05/21 21:19:06]

I believe this is safe. The purpose of the handler is to implement the guts of
the node and the audio node (which encapsulates the JS object) is just a thin
wrapper to the handler.

+tkent to verify.

[tkent, 2015/05/22 00:47:12]

Yes, it's ok to touch handlers from the main thread if we correctly avoid races.

+    }
+
+    double currentTime() const
+    {
+        return m_destinationNode ? m_destinationNode->audioDestinationHandler().currentTime() : 0;
+    }
 
     float sampleRate() const { return m_destinationNode ? m_destinationNode->handler().sampleRate() : 0; }
 
@@ -311,9 +314,6 @@ private:
     // The Promise that is returned by close();
     RefPtrWillBeMember<ScriptPromiseResolver> m_closeResolver;
 
-    // Follows the destination's currentSampleFrame, but might be slightly behind due to locking.
-    size_t m_cachedSampleFrame;
-
     // Tries to handle AudioBufferSourceNodes that were started but became disconnected or was never
     // connected. Because these never get pulled anymore, they will stay around forever. So if we
     // can, try to stop them so they can be collected.