[Arguments] Introduce a new backing store for non-strict arguments objects.

src/ic.cc

Index: src/ic.cc
diff --git a/src/ic.cc b/src/ic.cc
index 7e87b1b5fb45c315116a10cd16ce7cc6e8180ffa..e64f62ca44c8fc23f2658b20cb73bd835ebc889b 100644
--- a/src/ic.cc
+++ b/src/ic.cc
@@ -1253,8 +1253,13 @@ MaybeObject* KeyedLoadIC::Load(State state,
   }
 
   // Do not use ICs for objects that require access checks (including
-  // the global object).
+  // the global object) nor for non-strict arguments objects.
   bool use_ic = FLAG_use_ic && !object->IsAccessCheckNeeded();
+  if (use_ic && object->IsJSObject()) {
+    Heap* heap = Handle<JSObject>::cast(object)->GetHeap();
+    Map* elements_map = Handle<JSObject>::cast(object)->elements()->map();
+    use_ic = (elements_map != heap->non_strict_arguments_elements_map());
+  }
 
   if (use_ic) {
     Code* stub = generic_stub();