Oilpan: remove consts when checking GC-class convertibility.

Source/platform/heap/ThreadState.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 63 matching lines @@
 // rid of it if it is fast enough to go through thread-local storage
 // always.
 enum ThreadAffinity {
     AnyThread,
     MainThreadOnly,
 };
 
 class Node;
 class CSSValue;
 
-template<typename T, bool derivesNode = WTF::IsSubclass<T, Node>::value> struct DefaultThreadingTrait;
+template<typename T, bool derivesNode = WTF::IsSubclass<typename WTF::RemoveConst<T>::Type, Node>::value> struct DefaultThreadingTrait;
 
 template<typename T>
 struct DefaultThreadingTrait<T, false> {
     static const ThreadAffinity Affinity = AnyThread;
 };
 
 template<typename T>
 struct DefaultThreadingTrait<T, true> {
     static const ThreadAffinity Affinity = MainThreadOnly;
 };
@@ skipping 501 matching lines @@
 };
 
 template<> class ThreadStateFor<AnyThread> {
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 }
 
 #endif // ThreadState_h