webrtc: update expected return values for catalina

As of r708260 on Catalina these methods return the
SYSTEM_PERMISSION_DENIED rather than PERMISSION_DENIED.

Bug: 998755
Change-Id: I8fa29f08a93ec1b4df5cfd15d2343154f1985f81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879774
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709152}