Add a VM defined class MirrorReference as an opaque pointer for Dart code to VM internal objects.

runtime/vm/symbols.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_SYMBOLS_H_
 #define VM_SYMBOLS_H_
 
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
 
@@ skipping 187 matching lines @@
   V(_ExternalInt64Array, "_ExternalInt64Array")                                \
   V(_ExternalUint64Array, "_ExternalUint64Array")                              \
   V(_ExternalFloat32x4Array, "_ExternalFloat32x4Array")                        \
   V(_ExternalFloat32Array, "_ExternalFloat32Array")                            \
   V(_ExternalFloat64Array, "_ExternalFloat64Array")                            \
   V(ByteData, "ByteData")                                                      \
   V(ByteDataDot, "ByteData.")                                                  \
   V(ByteDataDotview, "ByteData.view")                                          \
   V(_ByteDataView, "_ByteDataView")                                            \
   V(_WeakProperty, "_WeakProperty")                                            \
+  V(_MirrorReference, "_MirrorReference")                                      \
   V(InvocationMirror, "_InvocationMirror")                                     \
   V(AllocateInvocationMirror, "_allocateInvocationMirror")                     \
   V(toString, "toString")                                                      \
   V(_ReceivePortImpl, "_ReceivePortImpl")                                      \
   V(_lookupReceivePort, "_lookupReceivePort")                                  \
   V(_handleMessage, "_handleMessage")                                          \
   V(_SendPortImpl, "_SendPortImpl")                                            \
   V(_create, "_create")                                                        \
   V(_id, "_id")                                                                \
   V(_get_or_create, "_get_or_create")                                          \
@@ skipping 241 matching lines @@
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_