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 b4a4fe7fda2c423c6450ee513d3d127472c0b63e..8f68917c319bdd3382fcf0b7a3d6adfff3e928c6 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -699,6 +699,8 @@ class MarkCompactCollector {
 
   void EnsureSweepingCompleted();
 
+  void SweepOrWaitUntilSweepingCompleted(Page* page);
+
   // 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.
@@ -979,6 +981,7 @@ class MarkCompactCollector {
   List<Code*> invalidated_code_;
 
   base::SmartPointer<FreeList> free_list_old_space_;
+  base::SmartPointer<FreeList> free_list_code_space_;
 
   friend class Heap;
 };