Fix/implement new write barrier for x64.

src/write-buffer.h

 // Copyright 2010 the V8 project authors. 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 23 matching lines @@
 #include "platform.h"
 
 namespace v8 {
 namespace internal {
 
 
 // Used to implement the write barrier by collecting addresses of pointers
 // between spaces.
 class WriteBuffer : public AllStatic {
  public:
-  static Address TopAddress() { return reinterpret_cast<Address>(&top_); }
+  static inline Address TopAddress();
 
   static void Setup();
   static void TearDown();
 
-  static inline void Mark(Address addr) {
-    *top_++ = addr;
-    if ((reinterpret_cast<uintptr_t>(top_) & kWriteBufferOverflowBit) != 0) {
-      ASSERT(top_ == limit_);
-      Compact();
-    } else {
-      ASSERT(top_ < limit_);
-    }
-  }
+  static inline void Mark(Address addr);
 
   static const int kWriteBufferOverflowBit = 1 << 16;
   static const int kWriteBufferSize = kWriteBufferOverflowBit;
   static const int kHashMapLengthLog2 = 12;
   static const int kHashMapLength = 1 << kHashMapLengthLog2;
 
   static void Compact();
 
  private:
-  static Address* top_;
   static Address* start_;
   static Address* limit_;
   static VirtualMemory* virtual_memory_;
   static uintptr_t* hash_map_1_;
   static uintptr_t* hash_map_2_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_WRITE_BARRIER_H_