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 093660a768604efae771441afdba25d9de210a63..ef947c95f780bcbd5a552f0c84565ae3b2a06236 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1050,7 +1050,7 @@ 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 {
@@ -1951,7 +1951,7 @@ class Heap {
     return heap_size_mb / kMbPerMs;
   }
 
-  void AdvanceIdleIncrementalMarking(intptr_t step_size);
+  void AdvanceIdleIncrementalMarking(int idle_time_in_ms);
 
   void ClearObjectStats(bool clear_last_time_stats = false);