Remove remaining uses of null's absolute address from non-IA32.

runtime/vm/object.cc

 // Copyright (c) 2012, 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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 13842 matching lines @@
       set_filled_entry_count(filled_entry_count() + 1);
       return;
     }
     i = (i + 1) & id_mask;
   } while (i != index);
   UNREACHABLE();
 }
 
 
 const char* MegamorphicCache::ToCString() const {
-  return "";
+  return "MegamorphicCache";
 }
 
 
 void MegamorphicCache::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Object::PrintJSONImpl(stream, ref);
 }
 
 
 RawSubtypeTestCache* SubtypeTestCache::New() {
   ASSERT(Object::subtypetestcache_class() != Class::null());
@@ skipping 7561 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart