[heap] Refactor evacuation for young and old gen into visitors.

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 d0fb955d8bc7499a1cbbbbedc22fd4a406737275..e950e7217c2a158845a3d52dc87e5514a017015f 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -329,6 +329,15 @@ class ThreadLocalTop;
 // Mark-Compact collector
 class MarkCompactCollector {
  public:
+  enum IterationMode {
+    kKeepMarking,
+    kClearMarkbits,
+  };
+
+  class HeapObjectVisitor;
+  class EvacuateNewSpaceVisitor;
+  class EvacuateOldSpaceVisitor;
+
   static void Initialize();
 
   void SetUp();
@@ -699,14 +708,13 @@ class MarkCompactCollector {
   // regions to each space's free list.
   void SweepSpaces();
 
-  int DiscoverAndEvacuateBlackObjectsOnPage(NewSpace* new_space,
-                                            NewSpacePage* p);
+  // Iterates through all live objects on a page using marking information.
+  // Returns whether all objects have successfully been visited.
+  bool IterateLiveObjectsOnPage(MemoryChunk* page, HeapObjectVisitor* visitor,
+                                IterationMode mode);
 
   void EvacuateNewSpace();
 
-  bool EvacuateLiveObjectsFromPage(Page* p, PagedSpace* target_space,
-                                   SlotsBuffer** evacuation_slots_buffer);
-
   void AddEvacuationSlotsBufferSynchronized(
       SlotsBuffer* evacuation_slots_buffer);