[heap] Implement simple marking in the concurrent marking thread.

src/heap/marking.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_MARKING_H
 #define V8_MARKING_H
 
 #include "src/utils.h"
 
 namespace v8 {
@@ skipping 25 matching lines @@
   }
 
   inline void Set() { *cell_ |= mask_; }
   inline bool Get() { return (*cell_ & mask_) != 0; }
   inline void Clear() { *cell_ &= ~mask_; }
 
   CellType* cell_;
   CellType mask_;
 
   friend class IncrementalMarking;
+  friend class ConcurrentMarkingMarkbits;
   friend class Marking;
 };
 
 // Bitmap is a sequence of cells each containing fixed number of bits.
 class Bitmap {
  public:
   static const uint32_t kBitsPerCell = 32;
   static const uint32_t kBitsPerCellLog2 = 5;
   static const uint32_t kBitIndexMask = kBitsPerCell - 1;
   static const uint32_t kBytesPerCell = kBitsPerCell / kBitsPerByte;
@@ skipping 298 matching lines @@
   }
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Marking);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MARKING_H_