Reduce imprecision of incremental marking.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 06544030134a343661d286c3a46e7e757a773347..7bfb9179f7122049b1f15262b127bf0b283c63a6 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1412,6 +1412,10 @@ class Heap {
   void QueueMemoryChunkForFree(MemoryChunk* chunk);
   void FreeQueuedChunks();
 
+  // Completely clear the Instanceof cache (to stop it keeping objects alive
+  // around a GC).
+  inline void CompletelyClearInstanceofCache();
+
  private:
   Heap();
 
@@ -1655,10 +1659,6 @@ class Heap {
   // Code to be run before and after mark-compact.
   void MarkCompactPrologue();
 
-  // Completely clear the Instanceof cache (to stop it keeping objects alive
-  // around a GC).
-  inline void CompletelyClearInstanceofCache();
-
   // Record statistics before and after garbage collection.
   void ReportStatisticsBeforeGC();
   void ReportStatisticsAfterGC();