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 d9d9d1a1945dac466b3f220fe37c4bdeba08a06b..d2b14775ea9c2bf861754e6e393c8fe0fb35803b 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1049,7 +1049,7 @@ 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 {
@@ -1950,7 +1950,7 @@ 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);