Implement IDL surface for RTCDtlsTransport

This provides the IDL surface only, there is no connection to the
underlying objects.

Bug: 907849
Change-Id: Ie11bac767c6a26628c1bc757d2529f1192a07e40
Reviewed-on: https://chromium-review.googlesource.com/c/1348064
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610730}
10 files changed