Don't overload FreeListElement for become.

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/growable_array.h"
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
@@ skipping 256 matching lines @@
   V(_ExternalFloat64Array, "_ExternalFloat64Array")                            \
   V(_ExternalFloat64x2Array, "_ExternalFloat64x2Array")                        \
   V(ByteData, "ByteData")                                                      \
   V(ByteDataDot, "ByteData.")                                                  \
   V(ByteDataDot_view, "ByteData._view")                                        \
   V(_ByteDataView, "_ByteDataView")                                            \
   V(ByteBuffer, "ByteBuffer")                                                  \
   V(ByteBufferDot_New, "ByteBuffer._New")                                      \
   V(_WeakProperty, "_WeakProperty")                                            \
   V(_MirrorReference, "_MirrorReference")                                      \
+  V(FreeListElement, "FreeListElement")                                        \
+  V(ForwardingCorpse, "ForwardingCorpse")                                      \
   V(InvocationMirror, "_InvocationMirror")                                     \
   V(AllocateInvocationMirror, "_allocateInvocationMirror")                     \
   V(toString, "toString")                                                      \
   V(_lookupHandler, "_lookupHandler")                                          \
   V(_handleMessage, "_handleMessage")                                          \
   V(DotCreate, "._create")                                                     \
   V(DotWithType, "._withType")                                                 \
   V(_get, "_get")                                                              \
   V(RangeError, "RangeError")                                                  \
   V(DotRange, ".range")                                                        \
@@ skipping 387 matching lines @@
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_