amp-video-docking causes a CLS on floating/docking

## What's the issue?
When testing with several video players (including amp-video and amp-youtube) amp-video-docking incurs a CLS and increases the score in Web Vitals by ~.026 on float and ~.015 on docking.

## How do we reproduce the issue?

https://jsbin.com/sudacim/edit?html,output

1. Select the player you wish to test.
2. Press play
3. Scroll until it floats, docks.
4. Check the console

## What browsers are affected?
Tested on Chrome as it pertains to Web Vitals

## Which AMP version is affected?
0.1