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.h

Index: third_party/tcmalloc/chromium/src/google/malloc_hook.h
===================================================================
--- third_party/tcmalloc/chromium/src/google/malloc_hook.h	(revision 88058)
+++ third_party/tcmalloc/chromium/src/google/malloc_hook.h	(working copy)
@@ -169,7 +169,7 @@
   inline static PreSbrkHook SetPreSbrkHook(PreSbrkHook hook) {
     return MallocHook_SetPreSbrkHook(hook);
   }
-  inline static void InvokePreSbrkHook(ptrdiff_t increment);
+  inline static void InvokePreSbrkHook(std::ptrdiff_t increment);
 
   // The SbrkHook is invoked whenever sbrk is called -- except when
   // the increment is 0.  This is because sbrk(0) is often called
@@ -180,7 +180,7 @@
   inline static SbrkHook SetSbrkHook(SbrkHook hook) {
     return MallocHook_SetSbrkHook(hook);
   }
-  inline static void InvokeSbrkHook(const void* result, ptrdiff_t increment);
+  inline static void InvokeSbrkHook(const void* result, std::ptrdiff_t increment);
 
   // Get the current stack trace.  Try to skip all routines up to and
   // and including the caller of MallocHook::Invoke*.