Make GCTracer persistent.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 65167799ebc0afadb2741daeea83183ae78704cb..8eb0351d41b35f5ee51518b5ff6c14d0f0027c83 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -18,7 +18,6 @@ typedef bool (*IsAliveFunction)(HeapObject* obj, int* size, int* offset);
 
 // Forward declarations.
 class CodeFlusher;
-class GCTracer;
 class MarkCompactCollector;
 class MarkingVisitor;
 class RootMarkingVisitor;
@@ -528,7 +527,7 @@ class MarkCompactCollector {
 
   // Prepares for GC by resetting relocation info in old and map spaces and
   // choosing spaces to compact.
-  void Prepare(GCTracer* tracer);
+  void Prepare();
 
   // Performs a global garbage collection.
   void CollectGarbage();
@@ -542,10 +541,6 @@ class MarkCompactCollector {
 
   void AbortCompaction();
 
-  // 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_; }
-
 #ifdef DEBUG
   // Checks whether performing mark-compact collection.
   bool in_use() { return state_ > PREPARE_GC; }
@@ -745,10 +740,6 @@ class MarkCompactCollector {
 
   bool sequential_sweeping_;
 
-  // A pointer to the current stack-allocated GC tracer object during a full
-  // collection (NULL before and after).
-  GCTracer* tracer_;
-
   SlotsBufferAllocator slots_buffer_allocator_;
 
   SlotsBuffer* migration_slots_buffer_;