Add tests to verify behavior of the DtlsSrtpKeyAgreement constraint

The DtlsSrtpKeyAgreement constraint, when explicit false, sets
the deprecated SDES key negotiation mode.
This test verifies that:

- SDES mode can talk to SDES mode
- SDES mode can NOT talk to (normal) DTLS mode
- The only legitimate syntaxes for the constraint are "old style"

This helps limit the number of patterns we have to look for
when evaluating whether the deprecation of the feature is working.

Bug: 804275
Change-Id: I0ea05af6eb4cb2ffd1f7d2fd8b48d64af49cb63e
Reviewed-on: https://chromium-review.googlesource.com/877891
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530850}
1 file changed