Initial UserTag and dart:profiler library

runtime/vm/raw_object.cc

Index: runtime/vm/raw_object.cc
diff --git a/runtime/vm/raw_object.cc b/runtime/vm/raw_object.cc
index acf25542488fb0d3ac3fcbfcdfe54e880c6158ef..fbc9ad1c0b482652bf58fddfd044dcdfcfbecbc1 100644
--- a/runtime/vm/raw_object.cc
+++ b/runtime/vm/raw_object.cc
@@ -835,4 +835,14 @@ intptr_t RawMirrorReference::VisitMirrorReferencePointers(
   return MirrorReference::InstanceSize();
 }
 
+
+intptr_t RawUserTag::VisitUserTagPointers(
+    RawUserTag* raw_obj, ObjectPointerVisitor* visitor) {
+  // Make sure that we got here with the tagged pointer as this.
+  ASSERT(raw_obj->IsHeapObject());
+  visitor->VisitPointers(raw_obj->from(), raw_obj->to());
+  return UserTag::InstanceSize();
+}
+
+
 }  // namespace dart