C++11: Use type aliases instead of typedefs

util/file/fd_io.cc

Index: util/file/fd_io.cc
diff --git a/util/file/fd_io.cc b/util/file/fd_io.cc
index 95257d83d758b056cebbd12e63b6a89ec9007520..270539c404440609a6d54f76f939f7ecf203ed3e 100644
--- a/util/file/fd_io.cc
+++ b/util/file/fd_io.cc
@@ -23,16 +23,16 @@
 namespace {
 
 struct ReadTraits {
-  typedef void* VoidBufferType;
-  typedef char* CharBufferType;
+  using VoidBufferType = void*;
+  using CharBufferType = char*;
   static ssize_t Operate(int fd, CharBufferType buffer, size_t size) {
     return read(fd, buffer, size);
   }
 };
 
 struct WriteTraits {
-  typedef const void* VoidBufferType;
-  typedef const char* CharBufferType;
+  using VoidBufferType = const void*;
+  using CharBufferType = const char*;
   static ssize_t Operate(int fd, CharBufferType buffer, size_t size) {
     return write(fd, buffer, size);
   }