Fullscreen video environment dim is lighter than Private Browsing environment dim

[cvan]

Hardware

Oculus Go
9e66e70

Steps to Reproduce

1. Open Private Browsing mode (from the Tray).
2. Notice the opacity of the environment dim.
3. Launch https://webxr.sh/media.
4. Open test case #5.
5. Press the Fullscreen icon on the <video controls> element.
6. Notice the opacity of the environment dim becomes lighter than the dim of the environment when Private Browsing mode is engaged outside of Fullscreen Mode.

Current Behavior

The opacity of the environment dim becomes lighter than the dim of the environment when Private Browsing mode is engaged outside of Fullscreen Mode.

Expected Behavior

The opacity of the environment dim becomes darker than the dim of the environment when Private Browsing mode is engaged outside of Fullscreen Mode.

Possible Solution

Possibly add more purple too.

Context

See these related issues:

• Tray doesn't indicate private icon on when restoring a private mode session #671 (comment)
• Private browsing Interaction colors are inconsistent #774
• Implement Sunrise/Sunset (mapped to brightening/dimming scene) when entering/exiting Private Mode #389

[cvan]

FWIW, I discovered today that Oculus Browser does the same exact thing (unless you manually change the Fullscreen Controls' Brightness settings to the Darkest mode). Heh.

We should still fix this. But I found it interesting. And it made me realise we should probably take into account the following dims from:

1. Private Browsing dim +
2. Fullscreen dim +
3. Brightness (via Fullscreen Controls) dim

Oh, and a dim for a (FxR-level) Permission Prompt when one appears (probably during Private Browsing, or could happen during a Pointer-Lock + Fullscreen session).