Make setting length on arrays faster.

src/objects-inl.h

 // Copyright 2006-2008 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 2755 matching lines @@
 bool JSObject::HasNamedInterceptor() {
   return map()->has_named_interceptor();
 }
 
 
 bool JSObject::HasIndexedInterceptor() {
   return map()->has_indexed_interceptor();
 }
 
 
+bool JSObject::AllowsSetElementsLength() {
+  bool result = elements()->IsFixedArray();
+  ASSERT(result == (!HasPixelElements() && !HasExternalArrayElements()));
+  return result;
+}
+
+
 StringDictionary* JSObject::property_dictionary() {
   ASSERT(!HasFastProperties());
   return StringDictionary::cast(properties());
 }
 
 
 NumberDictionary* JSObject::element_dictionary() {
   ASSERT(HasDictionaryElements());
   return NumberDictionary::cast(elements());
 }
@@ skipping 254 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_