Changes calculation of Scavenger's UsedInWords

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 906 matching lines @@
   survivor_end_ = top_;
 
   Scavenge();
 
   // It is possible for objects to stay in the new space
   // if the VM cannot create more pages for these objects.
   ASSERT((UsedInWords() == 0) || failed_to_promote_);
 }
 
 int64_t Scavenger::UsedInWords() const {
-  int64_t used_in_words = (top_ - FirstObjectStart()) >> kWordSizeLog2;
-  return used_in_words;
+  int64_t free_space_in_tlab = 0;
+  if (heap_->isolate()->IsMutatorThreadScheduled()) {
+    Thread* mutator_thread = heap_->isolate()->mutator_thread();
+    if (mutator_thread->HasActiveTLAB()) {
+      free_space_in_tlab =
+          (mutator_thread->end() - mutator_thread->top()) >> kWordSizeLog2;
+    }
+  }
+  int64_t max_space_used = (top_ - FirstObjectStart()) >> kWordSizeLog2;
+  return max_space_used - free_space_in_tlab;
 }
 
 }  // namespace dart