Remove unused private member variables found by clang -Wunused-private-field

src/store-buffer.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 192 matching lines @@
   friend class StoreBufferRebuildScope;
   friend class DontMoveStoreBufferEntriesScope;
 };
 
 
 class StoreBufferRebuildScope {
  public:
   explicit StoreBufferRebuildScope(Heap* heap,
                                    StoreBuffer* store_buffer,
                                    StoreBufferCallback callback)
-      : heap_(heap),
-        store_buffer_(store_buffer),
+      : store_buffer_(store_buffer),
         stored_state_(store_buffer->store_buffer_rebuilding_enabled_),
         stored_callback_(store_buffer->callback_) {
     store_buffer_->store_buffer_rebuilding_enabled_ = true;
     store_buffer_->callback_ = callback;
     (*callback)(heap, NULL, kStoreBufferStartScanningPagesEvent);
   }
 
   ~StoreBufferRebuildScope() {
     store_buffer_->callback_ = stored_callback_;
     store_buffer_->store_buffer_rebuilding_enabled_ = stored_state_;
     store_buffer_->CheckForFullBuffer();
   }
 
  private:
-  Heap* heap_;
   StoreBuffer* store_buffer_;
   bool stored_state_;
   StoreBufferCallback stored_callback_;
 };
 
 
 class DontMoveStoreBufferEntriesScope {
  public:
   explicit DontMoveStoreBufferEntriesScope(StoreBuffer* store_buffer)
       : store_buffer_(store_buffer),
         stored_state_(store_buffer->may_move_store_buffer_entries_) {
     store_buffer_->may_move_store_buffer_entries_ = false;
   }
 
   ~DontMoveStoreBufferEntriesScope() {
     store_buffer_->may_move_store_buffer_entries_ = stored_state_;
   }
 
  private:
   StoreBuffer* store_buffer_;
   bool stored_state_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_STORE_BUFFER_H_