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

src/layout-descriptor.h

Index: src/layout-descriptor.h
diff --git a/src/layout-descriptor.h b/src/layout-descriptor.h
index b2c61bb1c0ae4fceb884a7827890251ff65f5c85..cc149f18a431b48a004d0fdf7827e5d07fa2d811 100644
--- a/src/layout-descriptor.h
+++ b/src/layout-descriptor.h
@@ -28,6 +28,7 @@ class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
 
   // 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();