Reenable hanging tests on Mac.
Deadlock happened because the following locks were grabbed by two threads at the end of a test:
Thread 1:
CapturedFrameForwarder::AddOrUpdateSink() locks CapturedFrameForwarder::crit_ and calls
FrameGeneratorCapturer::AddOrUpdateSink() what tries to lock FrameGeneratorCapturer::lock_.
Thread 2:
FrameGeneratorCapturer::InsertFrame() locks FrameGeneratorCapturer::lock_ and calls
CapturedFrameForwarder::OnFrame() which tries to lock CapturedFrameForwarder::crit_.
So two threads are locking two same locks in different orders which may cause deadlock.
BUG=webrtc:7870
Review-Url: https://codereview.webrtc.org/2955083002
Cr-Commit-Position: refs/heads/master@{#18783}
267041c470