Connecting an AudioContext to a video causes the volume control to fail.

[Leon]

When you place a video on a webpage and then connect an AudioContext to it, the volume control is not working anymore, as opposed to others browsers in the industry.

This breaks ability to change volume easily while applying live audio modifications to a video.

Here is a simple example with a gain node:

let context = new window.AudioContext();
let gain_node = context.createGain();
let source = context.createMediaElementSource(document.getElementById('video'));
source.connect(gain_node);
gain_node.connect(context.destination);

[Radar WebKit Bug Importer]

<rdar://problem/85709135>