[es6] Object.getPrototypeOf should work with values

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index 4ba546b0fbca1765dd631af96f2c7ec0ef81759a..c1af69a46928eb3a55d495898d4a8bfc64fb7569 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -976,12 +976,9 @@ function DefineOwnProperty(obj, p, desc, should_throw) {
 }
 
 
-// ES5 section 15.2.3.2.
+// ES6 section 19.1.2.9
 function ObjectGetPrototypeOf(obj) {
-  if (!IS_SPEC_OBJECT(obj)) {
-    throw MakeTypeError("called_on_non_object", ["Object.getPrototypeOf"]);
-  }
-  return %_GetPrototype(obj);
+  return %_GetPrototype(TO_OBJECT_INLINE(obj));
 }
 
 // ES6 section 19.1.2.19.