Perform smaller marking steps incrementally in idle notification.

src/heap/gc-idle-time-handler.h

Index: src/heap/gc-idle-time-handler.h
diff --git a/src/heap/gc-idle-time-handler.h b/src/heap/gc-idle-time-handler.h
index 8dfe92d9f79f5510484978829bbbb7184a8b6c5e..9b7f2b59977f1e96d571be1dd843c13ba798b118 100644
--- a/src/heap/gc-idle-time-handler.h
+++ b/src/heap/gc-idle-time-handler.h
@@ -125,6 +125,9 @@ class GCIdleTimeHandler {
   // If contexts are disposed at a higher rate a full gc is triggered.
   static const double kHighContextDisposalRate;
 
+  // Incremental marking step time.
+  static const size_t kIncrementalMarkingStepTimeInMs = 1;
+
   class HeapState {
    public:
     void Print();