Create read only handles for empty_array and sentinel objects

lib/string.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/native_entry.h"
 #include "vm/object.h"
 #include "vm/symbols.h"
@@ skipping 14 matching lines @@
   Object& index_object = Object::Handle(isolate);
   for (intptr_t i = 0; i < array_len; i++) {
     index_object = a.At(i);
     if (!index_object.IsSmi()) {
       const Array& args = Array::Handle(Array::New(1));
       args.SetAt(0, index_object);
       Exceptions::ThrowByType(Exceptions::kArgument, args);
     }
     intptr_t value = Smi::Cast(index_object).Value();
     if (Utf::IsOutOfRange(value)) {
-      const Array& args = Array::Handle(Object::empty_array());
-      Exceptions::ThrowByType(Exceptions::kArgument, args);
+      Exceptions::ThrowByType(Exceptions::kArgument, Object::empty_array());
     } else {
       if (!Utf::IsLatin1(value)) {
         is_one_byte_string = false;
         if (Utf::IsSupplementary(value)) {
           utf16_len += 1;
         }
       }
     }
     utf32_array[i] = value;
   }
@@ skipping 146 matching lines @@
     if (!elem.IsString()) {
       const Array& args = Array::Handle(Array::New(1));
       args.SetAt(0, elem);
       Exceptions::ThrowByType(Exceptions::kArgument, args);
     }
   }
   return String::ConcatAll(strings);
 }
 
 }  // namespace dart