Make setting length on arrays faster.

src/objects.cc

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5260 matching lines @@
 
 static Object* ArrayLengthRangeError() {
   HandleScope scope;
   return Top::Throw(*Factory::NewRangeError("invalid_array_length",
                                             HandleVector<Object>(NULL, 0)));
 }
 
 
 Object* JSObject::SetElementsLength(Object* len) {
   // We should never end in here with a pixel or external array.
-  ASSERT(!HasPixelElements() && !HasExternalArrayElements());
+  ASSERT(AllowsSetElementsLength());
 
   Object* smi_length = len->ToSmi();
   if (smi_length->IsSmi()) {
     int value = Smi::cast(smi_length)->value();
     if (value < 0) return ArrayLengthRangeError();
     switch (GetElementsKind()) {
       case FAST_ELEMENTS: {
         int old_capacity = FixedArray::cast(elements())->length();
         if (value <= old_capacity) {
           if (IsJSArray()) {
@@ skipping 3110 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single beak point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif
 
 
 } }  // namespace v8::internal