Move map retaining to finalization of incremental marking.

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 45992be0af9e293bb5a6a1309ca96b12f8806664..f4983a7273e066b383542a097de315bf74e7b640 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -617,10 +617,6 @@ class MarkCompactCollector {
   // otherwise a map can die and deoptimize the code.
   void ProcessTopOptimizedFrame(ObjectVisitor* visitor);
 
-  // Retain dying maps for <FLAG_retain_maps_for_n_gc> garbage collections to
-  // increase chances of reusing of map transition tree in future.
-  void RetainMaps();
-
   // Collects a list of dependent code from maps embedded in optimize code.
   DependentCode* DependentCodeListFromNonLiveMaps();