[Story video] Videos fail to load in stories and flash multiple times

In the Discover carrousel stories that have videos can have those videos fail to load, while they flash multiple times indicating that the video is being reloaded over and over.

The issue lies in `flexible-bitrate.js` that will downgrade the video once (when the video takes more than 100ms to load) and then it will continually `updateOtherManagedAndPausedVideos_` which calls `load` again on the video.

This behavior can be reproed in https://codepen.io/mszylkowski/pen/JjbeEEr, where there's a gap between `waiting` and `playing` of more than 100ms when changing the sources.