Perform TODO(gc) cleanup for TODO-lockdown.

test/cctest/test-mark-compact.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 213 matching lines @@
   CHECK(Isolate::Current()->context()->global()->
         GetProperty(obj_name)->ToObjectChecked()->IsJSObject());
   obj = JSObject::cast(Isolate::Current()->context()->global()->
                        GetProperty(obj_name)->ToObjectChecked());
   prop_name =
       String::cast(HEAP->LookupAsciiSymbol("theSlot")->ToObjectChecked());
   CHECK(obj->GetProperty(prop_name) == Smi::FromInt(23));
 }
 
 
-// TODO(gc): compaction of map space is temporary removed from GC.
+// TODO(1600): compaction of map space is temporary removed from GC.
 #if 0
 static Handle<Map> CreateMap() {
   return FACTORY->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
 }
 
 
 TEST(MapCompact) {
   FLAG_max_map_space_pages = 16;
   InitializeVM();
 
@@ skipping 195 matching lines @@
   Handle<Object> object =
       global_handles->Create(HEAP->AllocateFixedArray(1)->ToObjectChecked());
 
   TestRetainedObjectInfo info;
   global_handles->AddObjectGroup(NULL, 0, &info);
   ASSERT(info.has_been_disposed());
 
   global_handles->AddImplicitReferences(
         Handle<HeapObject>::cast(object).location(), NULL, 0);
 }