Have ScriptPromiseResolver on the Oilpan heap always.

public/web/WebMIDIPermissionRequest.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 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef WebMIDIPermissionRequest_h
 #define WebMIDIPermissionRequest_h
 
 #include "../platform/WebCommon.h"
+#include "../platform/WebPrivatePtr.h"
 
 namespace blink {
 
 class MIDIAccessInitializer;
 class WebSecurityOrigin;
 
 // WebMIDIPermissionRequest encapsulates a WebCore MIDIAccessInitializer
 // object and represents a request from WebCore for permissions.
 // The request must not outlive the underlying initializer object.
 // In other words, the request must be canceled when the underlying
 // initializer dies while requesting,
 class WebMIDIPermissionRequest {
 public:
     BLINK_EXPORT WebMIDIPermissionRequest(const WebMIDIPermissionRequest& other)
-        : m_initializer(other.m_initializer) { }
+    {
+        assign(other);
+    }
+
+    ~WebMIDIPermissionRequest()
+    {
+        reset();
+    }
+
     BLINK_EXPORT WebSecurityOrigin securityOrigin() const;
     BLINK_EXPORT void setIsAllowed(bool);
 
     BLINK_EXPORT bool equals(const WebMIDIPermissionRequest&) const;
 
 #if BLINK_IMPLEMENTATION
     explicit WebMIDIPermissionRequest(MIDIAccessInitializer*);
 
-    MIDIAccessInitializer* midiAccessInitializer() const { return m_initializer; }
+    MIDIAccessInitializer* midiAccessInitializer() const { return m_private.get(); }
 #endif
 
 private:
-    MIDIAccessInitializer* m_initializer;
+    BLINK_EXPORT void reset();
+    BLINK_EXPORT void assign(const WebMIDIPermissionRequest&);
+
+    WebPrivatePtr<MIDIAccessInitializer> m_private;
 };
 
 inline bool operator==(const WebMIDIPermissionRequest& a, const WebMIDIPermissionRequest& b)
 {
     return a.equals(b);
 }
 
 inline bool operator!=(const WebMIDIPermissionRequest& a, const WebMIDIPermissionRequest& b)
 {
     return !(a == b);
 }
 
 } // namespace blink
 
 #endif // WebMIDIPermissionRequest_h