Make sure that memory reducer makes progress in incremental marking

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 6666b2c8238189ccfe269a8616c660550a69fe6a..690837c4f4cbe5c2b73e5f47a42ddf6b7496c2e1 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -867,6 +867,8 @@ class Heap {
       intptr_t step_size_in_bytes, double deadline_in_ms,
       IncrementalMarking::StepActions step_actions);
 
+  void FinalizeIncrementalMarkingIfComplete(const char* comment);
+
   inline void increment_scan_on_scavenge_pages() {
     scan_on_scavenge_pages_++;
     if (FLAG_gc_verbose) {
@@ -1650,6 +1652,8 @@ class Heap {
   bool HasHighFragmentation();
   bool HasHighFragmentation(intptr_t used, intptr_t committed);
 
+  bool ShouldOptimizeForMemoryUsage() { return optimize_for_memory_usage_; }
+
  protected:
   // Methods made available to tests.