blink: Cleanup class forward declarations

third_party/WebKit/Source/platform/heap/GarbageCollected.h

 // Copyright 2015 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 GarbageCollected_h
 #define GarbageCollected_h
 
 #include "platform/heap/ThreadState.h"
 #include "wtf/Allocator.h"
 #include "wtf/Assertions.h"
 #include "wtf/TypeTraits.h"
 
 namespace blink {
 
 template <typename T>
 class GarbageCollected;
+class HeapObjectHeader;
 class InlinedGlobalMarkingVisitor;
 class WrapperVisitor;
 
 // GC_PLUGIN_IGNORE is used to make the plugin ignore a particular class or
 // field when checking for proper usage.  When using GC_PLUGIN_IGNORE
 // a bug-number should be provided as an argument where the bug describes
 // what needs to happen to remove the GC_PLUGIN_IGNORE again.
 #if COMPILER(CLANG)
 #define GC_PLUGIN_IGNORE(bug) \
   __attribute__((annotate("blink_gc_plugin_ignore")))
@@ skipping 268 matching lines @@
   static FalseType isSizeofKnown(...);
   static T& t;
 
  public:
   static const bool value = sizeof(TrueType) == sizeof(isSizeofKnown(&t));
 };
 
 }  // namespace blink
 
 #endif