Use actual incremental marking throughput in IdleNotification to estimate marking step size.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index b10a47665cf96ae35dc6f8bc3d3d67f7dd7ea352..ad976821e100a58ea555d9514060caf6456f1dd2 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1068,7 +1068,7 @@ class Heap {
   void DisableInlineAllocation();
 
   // Implements the corresponding V8 API function.
-  bool IdleNotification(int hint);
+  bool IdleNotification(int idle_time_in_ms);
 
   // Declare all the root indices.  This defines the root list order.
   enum RootListIndex {
@@ -1969,7 +1969,8 @@ class Heap {
     return heap_size_mb / kMbPerMs;
   }
 
-  void AdvanceIdleIncrementalMarking(intptr_t step_size);
+  intptr_t EstimateMarkingStepSize(int idle_time_in_ms);
+  void AdvanceIdleIncrementalMarking(int idle_time_in_ms);
 
   void ClearObjectStats(bool clear_last_time_stats = false);