[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 cbd8e14679687455ad3dfe9e3f0459d50a8dc527..7a7915aa592b4a1e831b696c38b24e29197cc52f 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -979,12 +979,9 @@ 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.