Use private field chunk_

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/19495002

Patch from HaiTao Feng <haitao.feng@intel.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15709 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mark-compact.h

@@ -958,12 +958,12 @@ class MarkBitCellIterator BASE_EMBEDDED {
       : chunk_(chunk) {
     last_cell_index_ = Bitmap::IndexToCell(
         Bitmap::CellAlignIndex(
-            chunk->AddressToMarkbitIndex(chunk->area_end())));
-    cell_base_ = chunk->area_start();
+            chunk_->AddressToMarkbitIndex(chunk_->area_end())));
+    cell_base_ = chunk_->area_start();
     cell_index_ = Bitmap::IndexToCell(
         Bitmap::CellAlignIndex(
-            chunk->AddressToMarkbitIndex(cell_base_)));
-    cells_ = chunk->markbits()->cells();
+            chunk_->AddressToMarkbitIndex(cell_base_)));
+    cells_ = chunk_->markbits()->cells();
   }
 
   inline bool Done() { return cell_index_ == last_cell_index_; }