Preserve marking bits across scavenges if incremental marker is running.

src/mark-compact.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 161 matching lines @@
   // Type of functions to process non-live objects.
   typedef void (*ProcessNonLiveFunction)(HeapObject* object);
 
   // Set the global force_compaction flag, it must be called before Prepare
   // to take effect.
   static void SetFlags(int flags) {
     force_compaction_ = ((flags & Heap::kForceCompactionMask) != 0);
     sweep_precisely_ = ((flags & Heap::kMakeHeapIterableMask) != 0);
   }
 
+  static bool PreciseSweepingRequired() { return sweep_precisely_; }
 
   static void Initialize();
 
   // Prepares for GC by resetting relocation info in old and map spaces and
   // choosing spaces to compact.
   static void Prepare(GCTracer* tracer);
 
   // Performs a global garbage collection.
   static void CollectGarbage();
 
@@ skipping 245 matching lines @@
 
   friend class UnmarkObjectVisitor;
   static void UnmarkObject(HeapObject* obj);
 #endif
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_