Simplify the write barrier.

src/spaces.h

Index: src/spaces.h
===================================================================
--- src/spaces.h	(revision 9979)
+++ src/spaces.h	(working copy)
@@ -124,8 +124,8 @@
  public:
   typedef uint32_t CellType;
 
-  inline MarkBit(CellType* cell, CellType mask, bool data_only)
-      : cell_(cell), mask_(mask), data_only_(data_only) { }
+  inline MarkBit(CellType* cell, CellType mask)
+      : cell_(cell), mask_(mask) { }
 
   inline CellType* cell() { return cell_; }
   inline CellType mask() { return mask_; }
@@ -140,25 +140,18 @@
   inline bool Get() { return (*cell_ & mask_) != 0; }
   inline void Clear() { *cell_ &= ~mask_; }
 
-  inline bool data_only() { return data_only_; }
-
   inline MarkBit Next() {
     CellType new_mask = mask_ << 1;
     if (new_mask == 0) {
-      return MarkBit(cell_ + 1, 1, data_only_);
+      return MarkBit(cell_ + 1, 1);
     } else {
-      return MarkBit(cell_, new_mask, data_only_);
+      return MarkBit(cell_, new_mask);
     }
   }
 
  private:
   CellType* cell_;
   CellType mask_;
-  // This boolean indicates that the object is in a data-only space with no
-  // pointers.  This enables some optimizations when marking.
-  // It is expected that this field is inlined and turned into control flow
-  // at the place where the MarkBit object is created.
-  bool data_only_;
 };
 
 
@@ -214,10 +207,10 @@
     return reinterpret_cast<Bitmap*>(addr);
   }
 
-  inline MarkBit MarkBitFromIndex(uint32_t index, bool data_only = false) {
+  inline MarkBit MarkBitFromIndex(uint32_t index) {
     MarkBit::CellType mask = 1 << (index & kBitIndexMask);
     MarkBit::CellType* cell = this->cells() + (index >> kBitsPerCellLog2);
-    return MarkBit(cell, mask, data_only);
+    return MarkBit(cell, mask);
   }
 
   static inline void Clear(MemoryChunk* chunk);