Implement Function.prototype.toMethod.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 92d5ab5a2a346622a2368643e9da8faa0b11a34b..a2f77b1f0da8c788f4d119c42955a88338d3c94f 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7714,6 +7714,11 @@ class JSFunction: public JSObject {
   static void SetInstancePrototype(Handle<JSFunction> function,
                                    Handle<Object> value);
 
+  // Creates a new closure for the fucntion with the same bindings,
+  // bound values, and prototype. An equivalent of spec operations
+  // ``CloneMethod`` and ``CloneBoundFunction``.
+  static Handle<JSFunction> CloneClosure(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();