* Copy ensure_webcam_is_running.py from recipes repo
* Turn it into a wrapper that can launch another script
(fix_python_path is copied from test_env.py as _ForcePythonInterpreter)
* Support it in mb.py
* Add it to video_capture_unittests
No-Try: True
Bug: chromium:755660
Change-Id: I376724a77e443620724add7818592e9368d02079
Reviewed-on: https://webrtc-review.googlesource.com/77320
Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23275}