Defer changes to the channel count mode to the pre or post-render phase

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 feac957f31d1b8d0cd62f3ae97da6cc7d0857a32..7efdd5e33d729c7577f1f85b7bfdc69a9efd2b23 100644
--- a/Source/modules/webaudio/AudioContext.h
+++ b/Source/modules/webaudio/AudioContext.h
@@ -151,6 +151,12 @@ public:
     // Called right before handlePostRenderTasks() to handle nodes which need to be pulled even when they are not connected to anything.
     void processAutomaticPullNodes(size_t framesToProcess);
 
+    // Keep track of AudioNode's that have their channel count mode changed. We process the changes
+    // in the post rendering phase.
+    void addChangedChannelCountMode(AudioNode*);
+    void removeChangedChannelCountMode(AudioNode*);
+    void updateChangedChannelCountMode();
+
     // Keeps track of the number of connections made.
     void incrementConnectionCount()
     {
@@ -342,6 +348,11 @@ private:
 
     AsyncAudioDecoder m_audioDecoder;
 
+    // Collection of nodes where the channel count mode has changed. We want the channel count mode
+    // to change in the pre- or post-rendering phase so as not to disturb the running audio thread.
+    GC_PLUGIN_IGNORE("http://crbug.com/404527")
+    HashSet<AudioNode*> m_deferredCountModeChange;
+
     // This is considering 32 is large enough for multiple channels audio.
     // It is somewhat arbitrary and could be increased if necessary.
     enum { MaxNumberOfChannels = 32 };