VM: Reland Inline instance object hash code into object header on 64bit.

runtime/vm/freelist.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef RUNTIME_VM_FREELIST_H_
 #define RUNTIME_VM_FREELIST_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bit_set.h"
@@ skipping 38 matching lines @@
     static const ClassId kClassId = kFreeListElement;
     static bool IsInstance() { return true; }
 
    private:
     DISALLOW_ALLOCATION();
     DISALLOW_COPY_AND_ASSIGN(FakeInstance);
   };
 
  private:
   // This layout mirrors the layout of RawObject.
-  uword tags_;
+  uint32_t tags_;
+#if defined(HASH_IN_OBJECT_HEADER)
+  uint32_t hash_;
+#endif
   FreeListElement* next_;
 
   // Returns the address of the embedded size.
   intptr_t* SizeAddress() const {
     uword addr = reinterpret_cast<uword>(&next_) + kWordSize;
     return reinterpret_cast<intptr_t*>(addr);
   }
 
   // FreeListElements cannot be allocated. Instead references to them are
   // created using the AsElement factory method.
@@ skipping 55 matching lines @@
 
   // The largest available small size in bytes, or negative if there is none.
   intptr_t last_free_small_size_;
 
   DISALLOW_COPY_AND_ASSIGN(FreeList);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_FREELIST_H_