Remove unmarked entries from per context map caches.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 04d0ff69a7bf2daff0e99589bada4d81f120156d..179edba74e926a4ec8e65edc6c4449b413591e4d 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -306,6 +306,10 @@ class MarkCompactCollector {
   // flag on the marking stack.
   void RefillMarkingStack();
 
+  // After reachable maps have been marked process per context object
+  // literal map caches removing unmarked entries.
+  void ProcessMapCaches();
+
   // Callback function for telling whether the object *p is an unmarked
   // heap object.
   static bool IsUnmarkedHeapObject(Object** p);