Move ClearNonLiveReferences and friends into the gc.

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 1866c2aa71d706e701a48a25fb047ade8b87c7e9..a32c16b6f279226a298f1c0b333aeaaf594ff371 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -811,6 +811,11 @@ class MarkCompactCollector {
   void ClearNonLiveReferences();
   void ClearNonLivePrototypeTransitions(Map* map);
   void ClearNonLiveMapTransitions(Map* map, MarkBit map_mark);
+  void ClearMapTransitions(Map* map);
+  bool ClearMapBackPointer(Map* map);
+  void TrimDescriptorArray(Map* map, DescriptorArray* descriptors,
+                           int number_of_own_descriptors);
+  void TrimEnumCache(Map* map, DescriptorArray* descriptors);
 
   void ClearDependentCode(DependentCode* dependent_code);
   void ClearDependentICList(Object* head);