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

runtime/vm/isolate.h

 // 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.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/base_isolate.h"
@@ skipping 546 matching lines @@
 
   uword user_tag() const {
     return user_tag_;
   }
   static intptr_t user_tag_offset() {
     return OFFSET_OF(Isolate, user_tag_);
   }
   static intptr_t current_tag_offset() {
     return OFFSET_OF(Isolate, current_tag_);
   }
+  static intptr_t default_tag_offset() {
+    return OFFSET_OF(Isolate, default_tag_);
+  }
 
 #define ISOLATE_METRIC_ACCESSOR(type, variable, name, unit)                    \
   type* Get##variable##Metric() { return &metric_##variable##_; }
   ISOLATE_METRIC_LIST(ISOLATE_METRIC_ACCESSOR);
 #undef ISOLATE_METRIC_ACCESSOR
 
   static intptr_t IsolateListLength();
 
   RawGrowableObjectArray* tag_table() const { return tag_table_; }
   void set_tag_table(const GrowableObjectArray& value);
 
   RawUserTag* current_tag() const { return current_tag_; }
   void set_current_tag(const UserTag& tag);
 
+  RawUserTag* default_tag() const { return default_tag_; }
+  void set_default_tag(const UserTag& tag);
+
   Metric* metrics_list_head() {
     return metrics_list_head_;
   }
 
   void set_metrics_list_head(Metric* metric) {
     metrics_list_head_ = metric;
   }
 
 #if defined(DEBUG)
 #define REUSABLE_HANDLE_SCOPE_ACCESSORS(object)                                \
@@ skipping 93 matching lines @@
   TraceBuffer* trace_buffer_;
 
   IsolateProfilerData* profiler_data_;
   Mutex profiler_data_mutex_;
   InterruptableThreadState* thread_state_;
 
   VMTagCounters vm_tag_counters_;
   uword user_tag_;
   RawGrowableObjectArray* tag_table_;
   RawUserTag* current_tag_;
+  RawUserTag* default_tag_;
 
   Metric* metrics_list_head_;
 
   Counters counters_;
 
   // Isolate list next pointer.
   Isolate* next_;
 
   // Reusable handles support.
 #define REUSABLE_HANDLE_FIELDS(object)                                         \
@@ skipping 145 matching lines @@
   char* exception_callback_name_;
   uint8_t* serialized_args_;
   intptr_t serialized_args_len_;
   uint8_t* serialized_message_;
   intptr_t serialized_message_len_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_