Support slots recording for compaction during incremental marking.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 21a381055118886f041c31af9258ab1291d443bf..d8b5e1a6906255438df18acd3ba11e1d254aa391 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -265,7 +265,7 @@ class SlotsBuffer {
 
   void Clear();
   void Add(ObjectSlot slot);
-  void Iterate(ObjectVisitor* visitor);
+  void Update();
   void Report();
 
  private:
@@ -333,6 +333,8 @@ class MarkCompactCollector {
   // Performs a global garbage collection.
   void CollectGarbage();
 
+  bool StartCompaction();
+
   // During a full GC, there is a stack-allocated GCTracer that is used for
   // bookkeeping information.  Return a pointer to that tracer.
   GCTracer* tracer() { return tracer_; }
@@ -416,6 +418,10 @@ class MarkCompactCollector {
   // heap.
   bool sweep_precisely_;
 
+  // True if we are collecting slots to perform evacuation from evacuation
+  // candidates.
+  bool compacting_;
+
   // A pointer to the current stack-allocated GC tracer object during a full
   // collection (NULL before and after).
   GCTracer* tracer_;