Move some code from Runtime_GetPrototype into a new Object::GetPrototype.

src/runtime/runtime-object.cc

Index: src/runtime/runtime-object.cc
diff --git a/src/runtime/runtime-object.cc b/src/runtime/runtime-object.cc
index 87f416fd131ff0e7f2c3e658c2aabb6e6087e5a8..84becb41773663a6ef9b8d3f5a85d73d6a2bae74 100644
--- a/src/runtime/runtime-object.cc
+++ b/src/runtime/runtime-object.cc
@@ -157,22 +157,7 @@ RUNTIME_FUNCTION(Runtime_GetPrototype) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(Object, obj, 0);
-  // We don't expect access checks to be needed on JSProxy objects.
-  DCHECK(!obj->IsAccessCheckNeeded() || obj->IsJSObject());
-  PrototypeIterator iter(isolate, obj, PrototypeIterator::START_AT_RECEIVER);
-  Handle<Context> context(isolate->context());
-  do {
-    if (PrototypeIterator::GetCurrent(iter)->IsAccessCheckNeeded() &&
-        !isolate->MayAccess(context,
-                            PrototypeIterator::GetCurrent<JSObject>(iter))) {
-      return isolate->heap()->null_value();
-    }
-    iter.AdvanceIgnoringProxies();
-    if (PrototypeIterator::GetCurrent(iter)->IsJSProxy()) {
-      return *PrototypeIterator::GetCurrent(iter);
-    }
-  } while (!iter.IsAtEnd(PrototypeIterator::END_AT_NON_HIDDEN));
-  return *PrototypeIterator::GetCurrent(iter);
+  return *Object::GetPrototype(isolate, obj);
 }