[remoting WebRTC] Ensure SDP messages end with \r\n

This modifies the host to generate SDP messages with CRLF line-endings.
Both host and client already accept incoming SDP with CRLF or just LF.
However, the normalized form of SDP for signature-verification uses
just LF endings, and we need to maintain this for compatibilty.
So this CL introduces two normalized forms, one with CRLF endings for
sending SDP, and one with LF endings for signature calculation.

Bug: 830974
Test: Unittests, and manual end-to-end test using Chrome beta (M65).
Change-Id: I061637cf639af97184295e4a1b23aa4b663e246d
Reviewed-on: https://chromium-review.googlesource.com/1003773
Reviewed-by: Joe Downing <joedow@chromium.org>
Commit-Queue: Lambros Lambrou <lambroslambrou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549587}
4 files changed