- More use of pre-allocated read-only handles.

runtime/lib/object.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/exceptions.h"
 #include "vm/heap.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
@@ skipping 169 matching lines @@
     } else {
       type_name = type.UserVisibleName();
     }
     String& malformed_error_message =  String::Handle();
     if (malformed_error.IsNull()) {
       const String& dst_name = String::ZoneHandle(
           Symbols::New(Exceptions::kCastErrorDstName));
 
       Exceptions::CreateAndThrowTypeError(
           location, instance_type_name, type_name,
-          dst_name, String::Handle());
+          dst_name, Object::null_string());
     } else {
       ASSERT(FLAG_enable_type_checks);
       malformed_error_message = String::New(malformed_error.ToErrorCString());
       Exceptions::CreateAndThrowTypeError(
           location, instance_type_name, Symbols::Empty(),
           Symbols::Empty(), malformed_error_message);
     }
     UNREACHABLE();
   }
   return instance.raw();
 }
 
 
 DEFINE_NATIVE_ENTRY(AbstractType_toString, 1) {
   const AbstractType& type =
       AbstractType::CheckedHandle(arguments->NativeArgAt(0));
   return type.UserVisibleName();
 }
 
 }  // namespace dart