Merge up to 8597 to experimental/gc from the bleeding edge.

src/mark-compact.h

Index: src/mark-compact.h
===================================================================
--- src/mark-compact.h	(revision 8618)
+++ src/mark-compact.h	(working copy)
@@ -601,6 +601,10 @@
   // flag on the marking stack.
   void RefillMarkingDeque();
 
+  // 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);