1. Add user tag to the pointers traversed in the object store

runtime/vm/object_store.cc

 // Copyright (c) 2013, 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_store.h"
 
 #include "vm/exceptions.h"
 #include "vm/dart_entry.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 57 matching lines @@
     resume_capabilities_(GrowableObjectArray::null()),
     sticky_error_(Error::null()),
     unhandled_exception_handler_(String::null()),
     empty_context_(Context::null()),
     stack_overflow_(Instance::null()),
     out_of_memory_(Instance::null()),
     preallocated_stack_trace_(Stacktrace::null()),
     lookup_port_handler_(Function::null()),
     empty_uint32_array_(TypedData::null()),
     handle_message_function_(Function::null()),
-    library_load_error_table_(Array::null()),
-    default_tag_(UserTag::null()) {
+    library_load_error_table_(Array::null()) {
 }
 
 
 ObjectStore::~ObjectStore() {
 }
 
 
 void ObjectStore::VisitObjectPointers(ObjectPointerVisitor* visitor) {
   ASSERT(visitor != NULL);
   visitor->VisitPointers(from(), to());
@@ skipping 62 matching lines @@
       Stacktrace::Handle(Stacktrace::New(code_array, pc_offset_array));
   // Expansion of inlined functions requires additional memory at run time,
   // avoid it.
   stack_trace.set_expand_inlined(false);
   set_preallocated_stack_trace(stack_trace);
 
   return true;
 }
 
 }  // namespace dart