Oilpan: tidy up some inter-stack object references.

Source/modules/webaudio/AudioParam.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 40 matching lines @@
 // dies.
 class AudioParamHandler final : public ThreadSafeRefCounted<AudioParamHandler>, public AudioSummingJunction {
 public:
     static const double DefaultSmoothingConstant;
     static const double SnapThreshold;
 
     static PassRefPtr<AudioParamHandler> create(AbstractAudioContext& context, double defaultValue)
     {
         return adoptRef(new AudioParamHandler(context, defaultValue));
     }
-    DECLARE_TRACE();
+
     // This should be used only in audio rendering thread.
     AbstractAudioContext* context() const;
 
     // AudioSummingJunction
     void didUpdate() override { }
 
     AudioParamTimeline& timeline() { return m_timeline; }
 
     // Intrinsic value.
     float value();
@@ skipping 42 matching lines @@
     double m_value;
     double m_defaultValue;
 
     // Smoothing (de-zippering)
     double m_smoothedValue;
 
     AudioParamTimeline m_timeline;
 
     // We can't make this Persistent because of a reference cycle. It's safe to
     // access this field only when we're rendering audio.
+    GC_PLUGIN_IGNORE("509911")
     AbstractAudioContext& m_context;
 };
 
 // AudioParam class represents web-exposed AudioParam interface.
 class AudioParam final : public GarbageCollectedFinalized<AudioParam>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static AudioParam* create(AbstractAudioContext&, double defaultValue);
     DECLARE_TRACE();
     // |handler| always returns a valid object.
@@ skipping 14 matching lines @@
 private:
     AudioParam(AbstractAudioContext&, double defaultValue);
 
     RefPtr<AudioParamHandler> m_handler;
     Member<AbstractAudioContext> m_context;
 };
 
 } // namespace blink
 
 #endif // AudioParam_h