Initial UserTag and dart:profiler library

runtime/vm/tags.cc

Index: runtime/vm/tags.cc
diff --git a/runtime/vm/tags.cc b/runtime/vm/tags.cc
index f05aa22cc77cf3b478de034d91fd3d78e946f146..b1695b82fb0ee550c65cf85fdd79bf04154f0cfa 100644
--- a/runtime/vm/tags.cc
+++ b/runtime/vm/tags.cc
@@ -6,6 +6,8 @@
 
 #include "vm/isolate.h"
 #include "vm/json_stream.h"
+#include "vm/object.h"
+#include "vm/object_store.h"
 
 namespace dart {
 
@@ -78,4 +80,34 @@ void VMTagCounters::PrintToJSONObject(JSONObject* obj) {
   }
 }
 
+
+const char* UserTagHelper::TagName(uword tag_address) {
+  Isolate* isolate = Isolate::Current();
+  const Instance& tag = Instance::Handle(
+    isolate,
+    reinterpret_cast<RawInstance*>(tag_address));
+  if (tag.IsNull()) {
+    return "Default User Tag";
+  }
+  const Library& profiler_lib = Library::Handle(
+      isolate,
+      isolate->object_store()->profiler_library());
+  ASSERT(!profiler_lib.IsNull());
+  const String& tag_class_name = String::Handle(isolate, String::New("Tag"));
+  ASSERT(!tag_class_name.IsNull());
+  const Class& tag_class = Class::Handle(
+      profiler_lib.LookupClass(tag_class_name));
+  ASSERT(!tag_class.IsNull());
+  const String& label_field_name = String::Handle(String::New("label"));
+  ASSERT(!label_field_name.IsNull());
+  const Field& label_field =
+      Field::Handle(tag_class.LookupField(label_field_name));
+  ASSERT(!label_field.IsNull());
+  const Object& field = Object::Handle(tag.GetField(label_field));
+  ASSERT(!field.IsNull());
+  const String& label = String::Cast(field);
+  return label.ToCString();
+}
+
+
 }  // namespace dart