Oilpan: have DOMException be on the heap by default.

Source/core/streams/ReadableStreamReader.h

Index: Source/core/streams/ReadableStreamReader.h
diff --git a/Source/core/streams/ReadableStreamReader.h b/Source/core/streams/ReadableStreamReader.h
index c1417bbfb94a62c9282b63d31ba90838143f6b72..9fd7629d17463e38488ee042c591e3983e02566c 100644
--- a/Source/core/streams/ReadableStreamReader.h
+++ b/Source/core/streams/ReadableStreamReader.h
@@ -45,7 +45,7 @@ public:
     DECLARE_TRACE();
 
 private:
-    using ClosedPromise = ScriptPromiseProperty<Member<ReadableStreamReader>, ToV8UndefinedGenerator, RefPtrWillBeMember<DOMException>>;
+    using ClosedPromise = ScriptPromiseProperty<Member<ReadableStreamReader>, ToV8UndefinedGenerator, Member<DOMException>>;
 
     const Member<ReadableStream> m_stream;
     ReadableStream::State m_stateAfterRelease;