For duplicate style sheets with identical content, `StylesheetContents`
can be reused to avoid redundant parsing of the inline style sheets.
Since duplicate stylesheets is a common case with web components, this
change will significantly improve performance. Additionally, the cache
hit rate of stylo's `CascadeDataCache` can now be significantly
improved.
When shared `StylesheetContents` is modified, copy-on-write will occur
to avoid affecting other sharers. And then updates the references to
`CssRule` or `PropertyDeclarationBlock` stored in the CSSOMs to ensure
that modifications are made only on the new copy.
Signed-off-by: sharpshooter_pt <ibluegalaxy_taoj@163.com>
This is the CSSOM interface that represents a nested declarations rule.
https://drafts.csswg.org/css-nesting/#the-cssnestrule
Testing: `/_mozilla/mozilla/interfaces.https.html`. And once
`CSSStyleRule` becomes a `CSSGroupingRule` subclass, this will be
further covered by `/css/css-nestting/`.
This is part of #36245
Signed-off-by: Oriol Brufau <obrufau@igalia.com>
