Don't overload FreeListElement for become.

runtime/vm/scavenger.cc

 // Copyright (c) 2011, 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/scavenger.h"
 
 #include "vm/dart.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
@@ skipping 446 matching lines @@
   StoreBufferBlock* pending = isolate->store_buffer()->Blocks();
   intptr_t total_count = 0;
   while (pending != NULL) {
     StoreBufferBlock* next = pending->next();
     // Generated code appends to store buffers; tell MemorySanitizer.
     MSAN_UNPOISON(pending, sizeof(*pending));
     intptr_t count = pending->Count();
     total_count += count;
     while (!pending->IsEmpty()) {
       RawObject* raw_object = pending->Pop();
-      if (raw_object->IsFreeListElement()) {
-        // TODO(rmacnak): Forwarding corpse from become. Probably we should also
-        // visit the store buffer blocks during become, and mark any forwardees
-        // as remembered if their forwarders are remembered to satisfy the
-        // following assert.
+      if (raw_object->IsForwardingCorpse()) {
+        // A source object in a become was a remembered object, but we do
+        // not visit the store buffer during become to remove it.
         continue;
       }
       ASSERT(raw_object->IsRemembered());
       raw_object->ClearRememberedBit();
       visitor->VisitingOldObject(raw_object);
       raw_object->VisitPointers(visitor);
     }
     pending->Reset();
     // Return the emptied block for recycling (no need to check threshold).
     isolate->store_buffer()->PushBlock(pending, StoreBuffer::kIgnoreThreshold);
@@ skipping 404 matching lines @@
 }
 
 
 void Scavenger::FreeExternal(intptr_t size) {
   ASSERT(size >= 0);
   external_size_ -= size;
   ASSERT(external_size_ >= 0);
 }
 
 }  // namespace dart