A Page now has a StyleManager. The StyleManager currently answers two questions:
1 - Is an element hidden
2 - Does an element have pointer-events == none
This is used in calls such as element.checkVisibility which, on some pages, can
be called tens of thousands of times (often through other methods, like
element.getBoundingClientRect). This _can_ be a bottleneck.
The StyleManager keeps a list of rules. The rules include the selector,
specificity, and properties that we care about. Rules in a stylesheet that
contain no properties of interest are ignored. This is the first and likely
most significant optimization. Presumably, most CSS rules don't have a
display/visibility/opacity or pointer-events property.
The list is rules is cached until stylesheets are modified or delete. When this
happens, the StyleManager is flagged as "dirty" and rebuilt on-demand in the
next query. This is our second major optimization.
For now, to check if an element is visible, we still need to scan all rules.
But having a pre-build subset of all the rules is a first step.
The next step might be to optimize the matching, or possibly optimizing common
cases (e.g. id and/or simple class selector)
Refactors `CSSRule` to a union type for better type safety and updates
`CSSStyleRule` to use `CSSStyleProperties`. Adds comprehensive tests for
`insertRule`, `deleteRule`, and `replaceSync`.
- Remove scale, contain-intrinsic-size, animation-range, text-box-edge
from isTwoValueShorthand: these have asymmetric or 3-value semantics
that make "X X" → "X" collapse incorrect.
- Remove line-height from isLengthProperty: bare 0 is the unitless
number multiplier, not a length (Chrome serializes as "0" not "0px").
- Fix test: background-size "cover cover" is invalid CSS, use "auto auto".
Add missing properties to isLengthProperty (0→0px) and
isTwoValueShorthand (duplicate value collapse) maps based
on WPT test failures in css/css-sizing, css/css-align,
css/css-scroll-snap, css/css-logical, and others.
New length properties: scroll-margin/padding-*, column-width,
column-rule-width, grid-column/row-gap, outline, shape-margin,
offset-distance, translate, animation-range-*, block-step-size,
text-decoration-inset, and *-rule-*-inset (CSS Gaps).
New two-value shorthands: scroll-padding-block/inline,
scroll-snap-align, background-size, border-image-repeat,
mask-repeat/size, contain-intrinsic-size, scale, text-box-edge,
animation-range, grid-gap.
To reflect the current style attribute, CSSStyleDeclaration now parses
it on init.
Moreover, this PR synchronizes the element's style attribute with the
dynamic changes.
Instead of being mapped to HTMLUnknownElement, these will all be mapped to the
correct type. This is important for many WPT tests. But it's not impossible that
some script checks `if (x instanceof HTMLBaseElement)` and, without this, that
would error since HTMLBaseElement wouldn't be defined.
