Oilpan: tidy up some inter-stack object references.

Source/modules/webaudio/AudioParam.h

Index: Source/modules/webaudio/AudioParam.h
diff --git a/Source/modules/webaudio/AudioParam.h b/Source/modules/webaudio/AudioParam.h
index ee3dbf11b3212fb5f5b3a51b9b3dc195170e6dd1..3f6a2870a178762302795a7a9b8d2d6440c20c8d 100644
--- a/Source/modules/webaudio/AudioParam.h
+++ b/Source/modules/webaudio/AudioParam.h
@@ -58,7 +58,7 @@ public:
     {
         return adoptRef(new AudioParamHandler(context, defaultValue));
     }
-    DECLARE_TRACE();
+
     // This should be used only in audio rendering thread.
     AbstractAudioContext* context() const;
 
@@ -121,6 +121,7 @@ private:
 
     // 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;
 };