Add VM internal Dart class 'ClassID' used to manage class-ids of known classes. Next CL: add consta…

runtime/lib/class_id.cc

+// Copyright (c) 2014, 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 "platform/assert.h"
+#include "vm/bootstrap_natives.h"
+
+namespace dart {
+
+DEFINE_NATIVE_ENTRY(ClassID_getID, 1) {
+  const Instance& instance =
+      Instance::CheckedHandle(isolate, arguments->NativeArgAt(0));
+  return Smi::New(instance.GetClassId());
+}
+
+}  // namespace dart