Implement Function.prototype.toMethod.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d00941675789dbee0d2b7b132c5f051f34a741bd..22dbe26a51cd5a3414cace3d47f8a03972c6e1ea 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7732,6 +7732,8 @@ class JSFunction: public JSObject {
   static void SetInstancePrototype(Handle<JSFunction> function,
                                    Handle<Object> value);
 
+  static Handle<JSFunction> Copy(Handle<JSFunction> function);
+
   // After prototype is removed, it will not be created when accessed, and
   // [[Construct]] from this function will not be allowed.
   bool RemovePrototype();