[es6] Introduce spec compliant IsConstructor.

src/objects.cc

 // Copyright 2013 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 10701 matching lines @@
       JSObject::OptimizeAsPrototype(Handle<JSObject>::cast(value),
                                     FAST_PROTOTYPE);
     }
   }
   isolate->heap()->ClearInstanceofCache();
 }
 
 
 void JSFunction::SetPrototype(Handle<JSFunction> function,
                               Handle<Object> value) {
-  DCHECK(function->should_have_prototype());
+  DCHECK(function->IsConstructor());
   Handle<Object> construct_prototype = value;
 
   // If the value is not a JSReceiver, store the value in the map's
   // constructor field so it can be accessed.  Also, set the prototype
   // used for constructing objects to the original object prototype.
   // See ECMA-262 13.2.2.
   if (!value->IsJSReceiver()) {
     // Copy the map so this does not affect unrelated functions.
     // Remove map transitions because they point to maps with a
     // different prototype.
@@ skipping 6036 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8