Integration test for play recoverability from stream buffering

[clabe45]

When an input layer's source points to a WebRTC video or audio stream and when playing the movie the stream starts, then buffers due to network connectivity issues and then resumes, the movie should recover. One thing to check is that the movie's currentTime stopped progressing when the stream buffered. I suspect this test will fail. If it does, it's up to you if you want to fix the code or not. You can push the failing test and we can make a new issue for the bug, unless you'd rather fix the bug in the same PR.