Prevent excessive processing of weak maps while marking.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 0f20440062710bbc0e9108a7e1092476ac04cdbe..873534c2fa7838e3b28e7dff947069a8b7a021ab 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -841,14 +841,18 @@ class MarkCompactCollector {
   // is marked.
   void MarkImplicitRefGroups();
 
-  // Mark all objects which are reachable due to host application
-  // logic like object groups or implicit references' groups.
-  void ProcessExternalMarking(RootMarkingVisitor* visitor);
-
   // Mark objects reachable (transitively) from objects in the marking stack
   // or overflowed in the heap.
   void ProcessMarkingDeque();
 
+  // Mark objects reachable (transitively) from objects in the marking stack
+  // or overflowed in the heap.  This respects references only considered in
+  // the final atomic marking pause including the following:
+  //    - Processing of objects reachable through Harmony WeakMaps.
+  //    - Objects reachable due to host application logic like object groups
+  //      or implicit references' groups.
+  void ProcessEphemeralMarking(ObjectVisitor* visitor);
+
   // Mark objects reachable (transitively) from objects in the marking
   // stack.  This function empties the marking stack, but may leave
   // overflowed objects in the heap, in which case the marking stack's