Fix gcc 4.9.2 sign-compare error.

src/heap/spaces.h

 // Copyright 2011 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_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include "src/allocation.h"
 #include "src/atomic-utils.h"
 #include "src/base/atomicops.h"
@@ skipping 246 matching lines @@
       if (cells()[i] != 0) {
         return false;
       }
     }
     return true;
   }
 
   // Clears all bits starting from {cell_base_index} up to and excluding
   // {index}. Note that {cell_base_index} is required to be cell aligned.
   void ClearRange(uint32_t cell_base_index, uint32_t index) {
-    DCHECK_EQ(IndexInCell(cell_base_index), 0);
+    DCHECK_EQ(IndexInCell(cell_base_index), 0u);
     DCHECK_GE(index, cell_base_index);
     uint32_t start_cell_index = IndexToCell(cell_base_index);
     uint32_t end_cell_index = IndexToCell(index);
     DCHECK_GE(end_cell_index, start_cell_index);
     // Clear all cells till the cell containing the last index.
     for (uint32_t i = start_cell_index; i < end_cell_index; i++) {
       cells()[i] = 0;
     }
     // Clear all bits in the last cell till the last bit before index.
     uint32_t clear_mask = ~((1u << IndexInCell(index)) - 1);
@@ skipping 2731 matching lines @@
     count = 0;
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SPACES_H_