Oilpan: keep FormData on the heap by default.

Source/core/loader/BeaconLoader.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BeaconLoader_h
 #define BeaconLoader_h
 
 #include "core/CoreExport.h"
 #include "core/loader/PingLoader.h"
 #include "platform/heap/Handle.h"
@@ skipping 14 matching lines @@
 // staying alive. PingLoader providing the service.
 class CORE_EXPORT BeaconLoader final : public PingLoader {
     WTF_MAKE_NONCOPYABLE(BeaconLoader);
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED(BeaconLoader);
 public:
     ~BeaconLoader() override { }
 
     static bool sendBeacon(LocalFrame*, int, const KURL&, const String&, int&);
     static bool sendBeacon(LocalFrame*, int, const KURL&, PassRefPtr<DOMArrayBufferView>, int&);
     static bool sendBeacon(LocalFrame*, int, const KURL&, Blob*, int&);
-    static bool sendBeacon(LocalFrame*, int, const KURL&, PassRefPtrWillBeRawPtr<DOMFormData>, int&);
+    static bool sendBeacon(LocalFrame*, int, const KURL&, DOMFormData*, int&);
 
 private:
     class Sender;
 
     BeaconLoader(LocalFrame*, ResourceRequest&, const FetchInitiatorInfo&, StoredCredentials);
 
     RefPtr<SecurityOrigin> m_beaconOrigin;
 
     // WebURLLoaderClient
     void willSendRequest(WebURLLoader*, WebURLRequest&, const WebURLResponse&) override;
 };
 
 } // namespace blink
 
 #endif // BeaconLoader_h