[es6] Better support for built-ins subclassing.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 6c209b179207407623aa850d85587528c23b0a1c..676182f03b54be5328014e82c53175ac372f8d41 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2216,8 +2216,13 @@ class JSObject: public JSReceiver {
 
   // Get the header size for a JSObject.  Used to compute the index of
   // internal fields as well as the number of internal fields.
+  static inline int GetHeaderSize(InstanceType instance_type);
   inline int GetHeaderSize();
 
+  // Get the size of the header with internal fields of a JSObject.
+  // Used to calculate the instance size.
+  static inline int GetHeaderWithInternalFieldsSize(InstanceType instance_type);
+
   inline int GetInternalFieldCount();
   inline int GetInternalFieldOffset(int index);
   inline Object* GetInternalField(int index);
@@ -6786,10 +6791,10 @@ class SharedFunctionInfo: public HeapObject {
   int SourceSize();
 
   // Calculate the instance size.
-  int CalculateInstanceSize();
+  int CalculateInstanceSize(InstanceType instance_type);
 
   // Calculate the number of in-object properties.
-  int CalculateInObjectProperties();
+  int CalculateInObjectProperties(InstanceType instance_type);
 
   inline bool has_simple_parameters();
 
@@ -7286,6 +7291,8 @@ class JSFunction: public JSObject {
                             Handle<Object> prototype);
   inline bool has_initial_map();
   static void EnsureHasInitialMap(Handle<JSFunction> function);
+  static Handle<Map> EnsureDerivedHasInitialMap(
+      Handle<JSFunction> original_constructor, Handle<JSFunction> constructor);
 
   // Get and set the prototype property on a JSFunction. If the
   // function has an initial map the prototype is set on the initial