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

src/layout-descriptor.h

 // Copyright 2014 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_LAYOUT_DESCRIPTOR_H_
 #define V8_LAYOUT_DESCRIPTOR_H_
 
 #include <iosfwd>
 
 #include "src/objects.h"
@@ skipping 10 matching lines @@
 // Otherwise the field is considered tagged. If the queried bit lays "outside"
 // of the descriptor then the field is also considered tagged.
 // Once a layout descriptor is created it is allowed only to append properties
 // to it.
 class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
  public:
   V8_INLINE bool IsTagged(int field_index);
 
   // Returns true if this is a layout of the object having only tagged fields.
   V8_INLINE bool IsFastPointerLayout();
+  V8_INLINE static bool IsFastPointerLayout(Object* layout_descriptor);
 
   // Returns true if the layout descriptor is in non-Smi form.
   V8_INLINE bool IsSlowLayout();
 
   V8_INLINE static LayoutDescriptor* cast(Object* object);
   V8_INLINE static const LayoutDescriptor* cast(const Object* object);
 
   V8_INLINE static LayoutDescriptor* cast_gc_safe(Object* object);
 
   // Builds layout descriptor optimized for given |map| by |num_descriptors|
@@ skipping 76 matching lines @@
 
  private:
   bool all_fields_tagged_;
   int header_size_;
   LayoutDescriptor* layout_descriptor_;
 };
 }
 }  // namespace v8::internal
 
 #endif  // V8_LAYOUT_DESCRIPTOR_H_