Use mock.patch instead of setattr, deemed hackish and less robust.
As an additional benefit, mock is explictly activated and precisely scoped.
Bug: chromium:855108
Change-Id: I3644bb6773a4b95e50aa5b671292e108af1fd2e9
Reviewed-on: https://webrtc-review.googlesource.com/101660
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Yves Gerey <yvesg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24804}
4b9f3908ed