Replaced ptrdiff_t with std::ptrdiff_t in all files to enable build with gcc-4.6.0.

third_party/tcmalloc/chromium/src/memory_region_map.h

 /* Copyright (c) 2006, Google Inc.
  * 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
@@ skipping 305 matching lines @@
 
   // Hooks for MallocHook
   static void MmapHook(const void* result,
                        const void* start, size_t size,
                        int prot, int flags,
                        int fd, off_t offset);
   static void MunmapHook(const void* ptr, size_t size);
   static void MremapHook(const void* result, const void* old_addr,
                          size_t old_size, size_t new_size, int flags,
                          const void* new_addr);
-  static void SbrkHook(const void* result, ptrdiff_t increment);
+  static void SbrkHook(const void* result, std::ptrdiff_t increment);
 
   // Log all memory regions; Useful for debugging only.
   // Assumes Lock() is held
   static void LogAllLocked();
 
   DISALLOW_COPY_AND_ASSIGN(MemoryRegionMap);
 };
 
 #endif  // BASE_MEMORY_REGION_MAP_H_