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

third_party/tcmalloc/chromium/src/malloc_hook-inl.h

Index: third_party/tcmalloc/chromium/src/malloc_hook-inl.h
===================================================================
--- third_party/tcmalloc/chromium/src/malloc_hook-inl.h	(revision 88058)
+++ third_party/tcmalloc/chromium/src/malloc_hook-inl.h	(working copy)
@@ -170,7 +170,7 @@
   return base::internal::presbrk_hook_.Get();
 }
 
-inline void MallocHook::InvokePreSbrkHook(ptrdiff_t increment) {
+inline void MallocHook::InvokePreSbrkHook(std::ptrdiff_t increment) {
   MallocHook::PreSbrkHook hook = MallocHook::GetPreSbrkHook();
   if (hook != NULL && increment != 0) (*hook)(increment);
 }
@@ -180,7 +180,7 @@
 }
 
 inline void MallocHook::InvokeSbrkHook(const void* result,
-                                       ptrdiff_t increment) {
+                                       std::ptrdiff_t increment) {
   MallocHook::SbrkHook hook = MallocHook::GetSbrkHook();
   if (hook != NULL && increment != 0) (*hook)(result, increment);
 }