Don't overload FreeListElement for become.

runtime/vm/precompiler.cc

 // Copyright (c) 2015, 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 "vm/precompiler.h"
 
 #include "vm/aot_optimizer.h"
 #include "vm/assembler.h"
 #include "vm/ast_printer.h"
 #include "vm/branch_optimizer.h"
@@ skipping 348 matching lines @@
 
   // Allocated from C++.
   Class& cls = Class::Handle(Z);
   for (intptr_t cid = kInstanceCid; cid < kNumPredefinedCids; cid++) {
     ASSERT(isolate()->class_table()->IsValidIndex(cid));
     if (!isolate()->class_table()->HasValidClassAt(cid)) {
       continue;
     }
     if ((cid == kDynamicCid) ||
         (cid == kVoidCid) ||
-        (cid == kFreeListElement)) {
+        (cid == kFreeListElement) ||
+        (cid == kForwardingCorpse)) {
       continue;
     }
     cls = isolate()->class_table()->At(cid);
     AddInstantiatedClass(cls);
   }
 
   Dart_QualifiedFunctionName vm_entry_points[] = {
     // Functions
     { "dart:async", "::", "_setScheduleImmediateClosure" },
     { "dart:core", "::", "_completeDeferredLoads" },
@@ skipping 2466 matching lines @@
       CompilationPipeline::New(thread->zone(), function);
 
   ASSERT(FLAG_precompiled_mode);
   const bool optimized = function.IsOptimizable();  // False for natives.
   return PrecompileFunctionHelper(pipeline, function, optimized);
 }
 
 #endif  // DART_PRECOMPILER
 
 }  // namespace dart