Oilpan: remove unused IfWeakMember<T>.

Source/platform/heap/Heap.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 2390 matching lines @@
 struct GCInfoTrait<HeapLinkedHashSet<T, U, V> > : public GCInfoTrait<LinkedHashSet<T, U, V, HeapAllocator> > { };
 template<typename T, size_t inlineCapacity, typename U>
 struct GCInfoTrait<HeapListHashSet<T, inlineCapacity, U> > : public GCInfoTrait<ListHashSet<T, inlineCapacity, U, HeapListHashSetAllocator<T, inlineCapacity> > > { };
 template<typename T, size_t inlineCapacity>
 struct GCInfoTrait<HeapVector<T, inlineCapacity> > : public GCInfoTrait<Vector<T, inlineCapacity, HeapAllocator> > { };
 template<typename T, size_t inlineCapacity>
 struct GCInfoTrait<HeapDeque<T, inlineCapacity> > : public GCInfoTrait<Deque<T, inlineCapacity, HeapAllocator> > { };
 template<typename T, typename U, typename V>
 struct GCInfoTrait<HeapHashCountedSet<T, U, V> > : public GCInfoTrait<HashCountedSet<T, U, V, HeapAllocator> > { };
 
-template<typename T>
-struct IfWeakMember;
-
-template<typename T>
-struct IfWeakMember {
-    template<typename U>
-    static bool isDead(Visitor*, const U&) { return false; }
-};
-
-template<typename T>
-struct IfWeakMember<WeakMember<T> > {
-    static bool isDead(Visitor* visitor, const WeakMember<T>& t) { return !visitor->isAlive(t.get()); }
-};
-
 } // namespace blink
 
 #endif // Heap_h