Verify getContributingSources() does not return any CSRCs.

The previous test was, and always had been, completely broken. In a
loopback call scenario such as in WPT tests, no CSRCs are being
received so we should not expect them to. In order to properly test this
method one would need fakes, mocks or a server to receive CSRCs from.
This test is updated to test the only thing that we can test in Web
Platform Tests: in a loopback call, getContributingSources() returns an
empty list.

Bug: 893158
Change-Id: I18782ea7912001c012c98145500d8b3c5e95a7ba
Reviewed-on: https://chromium-review.googlesource.com/c/1404266
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621972}
2 files changed