Refactor 'dart:profiler' UserTag API

runtime/vm/object_store.h

 // 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.
 
 #ifndef VM_OBJECT_STORE_H_
 #define VM_OBJECT_STORE_H_
 
 #include "vm/object.h"
 
 namespace dart {
@@ skipping 379 matching lines @@
     lookup_port_handler_ = function.raw();
   }
 
   RawFunction* handle_message_function() const {
     return handle_message_function_;
   }
   void set_handle_message_function(const Function& function) {
     handle_message_function_ = function.raw();
   }
 
+  RawUserTag* default_tag() const {
+    return default_tag_;
+  }
+  void set_default_tag(const UserTag& tag) {
+    // Only set once.
+    ASSERT(default_tag_ == UserTag::null());
+    ASSERT(!tag.IsNull());
+    default_tag_ = tag.raw();
+  }
+  static intptr_t default_tag_offset() {
+    return OFFSET_OF(ObjectStore, default_tag_);
+  }
+
   // Visit all object pointers.
   void VisitObjectPointers(ObjectPointerVisitor* visitor);
 
   // Called to initialize objects required by the vm but which invoke
   // dart code.  If an error occurs then false is returned and error
   // information is stored in sticky_error().
   bool PreallocateObjects();
 
   static void Init(Isolate* isolate);
 
@@ skipping 63 matching lines @@
   RawGrowableObjectArray* pending_classes_;
   RawGrowableObjectArray* pending_functions_;
   RawError* sticky_error_;
   RawString* unhandled_exception_handler_;
   RawContext* empty_context_;
   RawInstance* stack_overflow_;
   RawInstance* out_of_memory_;
   RawStacktrace* preallocated_stack_trace_;
   RawFunction* lookup_port_handler_;
   RawFunction* handle_message_function_;
+  RawUserTag* default_tag_;
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&handle_message_function_);
   }
 
   friend class SnapshotReader;
 
   DISALLOW_COPY_AND_ASSIGN(ObjectStore);
 };
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_STORE_H_