Reland of "Enable inobject double fields unboxing for 64-bit archs."

src/objects.h

 // Copyright 2012 the V8 project 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 V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 5872 matching lines @@
   // [constructor]: points back to the function responsible for this map.
   DECL_ACCESSORS(constructor, Object)
 
   // [instance descriptors]: describes the object.
   DECL_ACCESSORS(instance_descriptors, DescriptorArray)
 
   // [layout descriptor]: describes the object layout.
   DECL_ACCESSORS(layout_descriptor, LayoutDescriptor)
   // |layout descriptor| accessor which can be used from GC.
   inline LayoutDescriptor* layout_descriptor_gc_safe();
+  inline bool HasFastPointerLayout() const;
 
   // |layout descriptor| accessor that is safe to call even when
   // FLAG_unbox_double_fields is disabled (in this case Map does not contain
   // |layout_descriptor| field at all).
   inline LayoutDescriptor* GetLayoutDescriptor();
 
   inline void UpdateDescriptors(DescriptorArray* descriptors,
                                 LayoutDescriptor* layout_descriptor);
   inline void InitializeDescriptors(DescriptorArray* descriptors,
                                     LayoutDescriptor* layout_descriptor);
@@ skipping 5076 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_