Log how long it took in DialpadFragment.onResult...

if it took more than 50 milliseconds.

I started to suspect that creating the tone generator may be to blame
for dialpad launch slowness, at least in the bug 6476832 case.

Let's add a log to verify the theory.

Change-Id: Ib9f46a78313199d495238a27a9996af081b2f2af