Reland concurrent sweeping of code space.

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 e212c9501dda037d90463adb6de3afbc79a4bc15..b2a41ce1f6733d2e47d72da51971454c61dfaf12 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -691,6 +691,8 @@ class MarkCompactCollector {
 
   void EnsureSweepingCompleted();
 
+  void EnsureSweepingCompleted(Page* page, PagedSpace* space);
+
   // If sweeper threads are not active this method will return true. If
   // this is a latency issue we should be smarter here. Otherwise, it will
   // return true if the sweeper threads are done processing the pages.
@@ -967,6 +969,7 @@ class MarkCompactCollector {
   List<Page*> evacuation_candidates_;
 
   base::SmartPointer<FreeList> free_list_old_space_;
+  base::SmartPointer<FreeList> free_list_code_space_;
 
   friend class Heap;
 };