Empty dtlsidentityservice.h/cc files added, to be removed once chromium gyp files don't reference it.

This is CL is part of an effort to land https://codereview.webrtc.org/1176383004 without breaking Chromium.
See bug for more information.

BUG=webrtc:4899

TBR=tommi@webrtc.org,magjed@webrtc.org

Review URL: https://codereview.webrtc.org/1276233006 .

Cr-Commit-Position: refs/heads/master@{#9697}
2 files changed