Have ScriptPromiseResolver on the Oilpan heap always.

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 6f5b7cda11aeaad2a57482bdb9d6e55180b5f338..bbe724b5b2345154a077fc05a01a21d0e36e9ce9 100644
--- a/Source/modules/webaudio/AudioContext.h
+++ b/Source/modules/webaudio/AudioContext.h
@@ -42,7 +42,7 @@ private:
     void stopRendering();
 
     unsigned m_contextId;
-    RefPtrWillBeMember<ScriptPromiseResolver> m_closeResolver;
+    Member<ScriptPromiseResolver> m_closeResolver;
 };
 
 }