This will no longer be true once we implement at-rules nested inside
style rules, for example:
```css
.foo {
color: yellow;
@media (min-width: 800px) {
color: orange;
}
}
```
If a rule gets its caches cleared because it's moved in the OM, then its
child rules' caches are likely invalid and need clearing too.
Assuming that caches only point "upwards", this will correctly clear
them all. For the time being that will be true.
This implements the `is_valid_in_the_current_context()` methods by
maintaining a stack of contexts, such as whether we're inside a style
rule, or an `@media` block, or the condition of a `@supports` rule.
This is implemented by using a GPU-accelerated surface for <canvas> when
a GPU context is available.
A side effect of this change is that all canvas modifications have to be
performed through Gfx::Painter, and whenever its content has to be
accessed, we need to take a snapshot of the corresponding GPU surface.
A new DrawPaintingSurface display list command is introduced to allow
cheap blitting of canvas content without having to read GPU surface
content into RAM.
Since the Vulkan context is currently only used by LibGfx, it could be
moved there to avoid having Vulkan as a dependency for everything that
uses LibCore.
Since the Metal context is currently only used by LibGfx, it could be
moved there to avoid having Metal as a dependency for everything that
uses LibCore.
This is required to share GPU context creation code between display list
player, which resides in LibWeb, and PainterSkia, which handles <canvas>
painting.
Chromium has a larger list of boolean attributes, and WPT depends on it.
We must also compare attribute names case-insensitively.
Note this method is only used by WebDriver.
We can't invalidate after the removal has taken effect, since that means
invalidation won't be able to find potentially affected siblings and
ancestors by traversing from the invalidation target.
While traversing the DOM tree, looking for nodes that need a style
update, we were recomputing style for every node visited along the way,
even nodes that didn't themselves need a style update (but one of their
descendants did).
This avoids a bunch of completely unnecessary style recomputation on
basically every website.
This class was being copied all over the place, however, most of these
cases can be easily prevented with `auto const&` or `NonnullRawPtr<>`.
It also didn't have a move constructor, causing `Vector` to copy on
every resize as well.
Removing all these copies results in an almost 15% increase in
performance for CSS parsing, as measured with callgrind.
