Add comments to vectors/hash sets of raw pointers to on-heap objects used in webaudio/

Source/modules/webaudio/AudioSummingJunction.h

Index: Source/modules/webaudio/AudioSummingJunction.h
diff --git a/Source/modules/webaudio/AudioSummingJunction.h b/Source/modules/webaudio/AudioSummingJunction.h
index b6a25be10629c5469437e4865e63792d98fa4d5b..e4db9907e55d2428fb6aa0a18740782e7be48db0 100644
--- a/Source/modules/webaudio/AudioSummingJunction.h
+++ b/Source/modules/webaudio/AudioSummingJunction.h
@@ -67,12 +67,16 @@ protected:
 
     // m_outputs contains the AudioNodeOutputs representing current connections which are not disabled.
     // The rendering code should never use this directly, but instead uses m_renderingOutputs.
+    // Oilpan: Since items are added to the hash set by the audio thread (not registered to Oilpan),
+    // we cannot use a HeapHashSet.
     HashSet<AudioNodeOutput*> m_outputs;
 
     // m_renderingOutputs is a copy of m_outputs which will never be modified during the graph rendering on the audio thread.
     // This is the list which is used by the rendering code.
     // Whenever m_outputs is modified, the context is told so it can later update m_renderingOutputs from m_outputs at a safe time.
     // Most of the time, m_renderingOutputs is identical to m_outputs.
+    // Oilpan: Since items are added to the vector by the audio thread (not registered to Oilpan),
+    // we cannot use a HeapVector.
     Vector<AudioNodeOutput*> m_renderingOutputs;
 
     // m_renderingStateNeedUpdating keeps track if m_outputs is modified.