Have ScriptPromiseResolver on the Oilpan heap always.

Source/modules/crypto/CryptoResultImpl.h

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 37 matching lines @@
 // The thread on which CryptoResultImpl was created on is referred to as the
 // "origin thread".
 //
 //  * At creation time there must be an active ExecutionContext.
 //  * The CryptoResult interface must only be called from the origin thread.
 //  * ref(), deref(), cancelled() and cancel() can be called from any thread.
 //  * One of the completeWith***() functions must be called, or the
 //    m_resolver will be leaked until the ExecutionContext is destroyed.
 class CryptoResultImpl final : public CryptoResult {
 public:
+    static CryptoResultImpl* create(ScriptState*);
+
     ~CryptoResultImpl();
 
-    static PassRefPtrWillBeRawPtr<CryptoResultImpl> create(ScriptState*);
-
     void completeWithError(WebCryptoErrorType, const WebString&) override;
     void completeWithBuffer(const void* bytes, unsigned bytesSize) override;
     void completeWithJson(const char* utf8Data, unsigned length) override;
     void completeWithBoolean(bool) override;
     void completeWithKey(const WebCryptoKey&) override;
     void completeWithKeyPair(const WebCryptoKey& publicKey, const WebCryptoKey& privateKey) override;
     bool cancelled() const override;
 
     // If called after completion (including cancellation) will return an empty
     // ScriptPromise.
     ScriptPromise promise();
 
+    DECLARE_VIRTUAL_TRACE();
+
 private:
     class Resolver;
     explicit CryptoResultImpl(ScriptState*);
 
     void clearResolver();
     void cancel();
 
-    // FIXME: ScriptPromiseResolver should not be exported.
-    // Instead, use ScriptPromise.
-    ScriptPromiseResolver* m_resolver;
+    Member<Resolver> m_resolver;
     volatile int m_cancelled;
 };
 
 } // namespace blink
 
 #endif