Reland "Adds resource path support for video files in scenario tests."

This is a reland of 8306a733f0dc45f19462268e29c90ada9f46b28e

Original change's description:
> Adds resource path support for video files in scenario tests.
> 
> Bug: webrtc:9510
> Change-Id: Id41a32325cc5b16b119e62fba483cec88f52975b
> Reviewed-on: https://webrtc-review.googlesource.com/c/123189
> Commit-Queue: Sebastian Jansson <srte@webrtc.org>
> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#26804}

Bug: webrtc:9510
Change-Id: I97a5568063569ca66d87f28204200a582d01e2e1
Reviewed-on: https://webrtc-review.googlesource.com/c/123960
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26836}