I think this is valid code, I found it while looking to workarounds for PR 14777.
template <typename T>
struct B
{
protected:
  typedef int M;
};

template <typename T>
struct A : B<T> {
  using typename B<T>::M;
  typedef M N;
  A (int = N ());
};

A<int> a = A<int> ();

In 3.3 (without the typename before B<T>::M as with gives a parse error), it gives a warning:
pr14777.cc:11: warning: `A<T>::M' is implicitly a typename
pr14777.cc:11: warning: implicit typename is deprecated, please see the 
   documentation for details

Note without templates this works:
struct B
{
protected:
  typedef int M;
};

struct A : B {
  using B::M;
  typedef M N;
  A (int = N ());
};

A a = A ();