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

third_party/tcmalloc/chromium/src/google/malloc_hook_c.h

 /* Copyright (c) 2008, 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 66 matching lines @@
 MallocHook_MunmapHook MallocHook_SetMunmapHook(MallocHook_MunmapHook hook);
 
 typedef void (*MallocHook_MremapHook)(const void* result,
                                       const void* old_addr,
                                       size_t old_size,
                                       size_t new_size,
                                       int flags,
                                       const void* new_addr);
 MallocHook_MremapHook MallocHook_SetMremapHook(MallocHook_MremapHook hook);
 
-typedef void (*MallocHook_PreSbrkHook)(ptrdiff_t increment);
+typedef void (*MallocHook_PreSbrkHook)(std::ptrdiff_t increment);
 MallocHook_PreSbrkHook MallocHook_SetPreSbrkHook(MallocHook_PreSbrkHook hook);
 
-typedef void (*MallocHook_SbrkHook)(const void* result, ptrdiff_t increment);
+typedef void (*MallocHook_SbrkHook)(const void* result, std::ptrdiff_t increment);
 MallocHook_SbrkHook MallocHook_SetSbrkHook(MallocHook_SbrkHook hook);
 
 #endif /* _MALLOC_HOOK_C_H_ */