Uncommit and shrink semi-spaces only on low allocation rate.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 8ecf7ae1328df4e495242eb777a128b1e7d6efc0..95d6c806580848dcad7b64008263aacc3debe6c1 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -2127,7 +2127,10 @@ class Heap {
 
   void SelectScavengingVisitorsTable();
 
-  void ReduceNewSpaceSize(GCIdleTimeAction action);
+  bool HasLowAllocationRate(GCIdleTimeHandler::HeapState heap_state);
+
+  void ReduceNewSpaceSize(GCIdleTimeAction action,
+                          GCIdleTimeHandler::HeapState heap_state);
 
   bool TryFinalizeIdleIncrementalMarking(
       double idle_time_in_ms, size_t size_of_objects,