Frédéric Wang acef313f3d Bug 1839313 - Add "fetchpriority" attribute to <img> element. r=smaug
This patch adds fetchpriority support for the `<img>` element, also
exposing the corresponding attribute in the WebIDL. As in D197493, we
try and minimize the change and rely on a mapping configurable under a
preference to ease future experiments. We use initial mapping
PRIORITY_LOW/PRIORITY_HIGH/PRIORITY_LOW for fetchpriority=low/high/auto
and allow further adjustments in the image code.

Internal fetchpriority mapping is covered by the following tests:
- `image-initial-load.h2.html` (typos fixed here)
- `image-dynamic-load.h2.html`

DOM tests are covered by the following tests (pref enabled to make them
pass):
- `idlharness.https.html`
- `attr-img-fetchpriority.html`

Differential Revision: https://phabricator.services.mozilla.com/D202222
2024-02-27 18:49:08 +00:00
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