[es6] Introduce spec compliant IsConstructor.

src/ic/ic.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ic/ic.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/base/bits.h"
@@ skipping 1141 matching lines @@
 
   if (receiver->IsStringWrapper() &&
       Name::Equals(isolate()->factory()->length_string(), lookup->name())) {
     StringLengthStub string_length_stub(isolate());
     return string_length_stub.GetCode();
   }
 
   // Use specialized code for getting prototype of functions.
   if (receiver->IsJSFunction() &&
       Name::Equals(isolate()->factory()->prototype_string(), lookup->name()) &&
-      Handle<JSFunction>::cast(receiver)->should_have_prototype() &&
+      receiver->IsConstructor() &&
       !Handle<JSFunction>::cast(receiver)
            ->map()
            ->has_non_instance_prototype()) {
     Handle<Code> stub;
     FunctionPrototypeStub function_prototype_stub(isolate());
     return function_prototype_stub.GetCode();
   }
 
   Handle<Map> map = receiver_map();
   Handle<JSObject> holder = lookup->GetHolder<JSObject>();
@@ skipping 1947 matching lines @@
     KeyedLoadICNexus nexus(vector, vector_slot);
     KeyedLoadIC ic(IC::EXTRA_CALL_FRAME, isolate, &nexus);
     ic.UpdateState(receiver, key);
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result, ic.Load(receiver, key));
   }
 
   return *result;
 }
 }  // namespace internal
 }  // namespace v8