Fixes bug in calculation of memory used by new space

runtime/vm/scavenger.cc

Index: runtime/vm/scavenger.cc
diff --git a/runtime/vm/scavenger.cc b/runtime/vm/scavenger.cc
index 336f9c9cc156b2ab953259ed43561f9e988f8419..0a17e7343cf51132d4ab91a596e5ad1082e745e1 100644
--- a/runtime/vm/scavenger.cc
+++ b/runtime/vm/scavenger.cc
@@ -948,4 +948,11 @@ void Scavenger::Evacuate() {
   ASSERT((UsedInWords() == 0) || failed_to_promote_);
 }
 
+int64_t Scavenger::UsedInWords() const {
+  uword saved_top = FlushTLS();
+  int64_t used_in_words = (top_ - FirstObjectStart()) >> kWordSizeLog2;
+  UnflushTLS(saved_top);
+  return used_in_words;
+}
+
 }  // namespace dart