Move the layout tree from GC allocation to refcounted ownership so
removed layout and paint subtrees are destroyed synchronously instead
of waiting for the next GC sweep. This dramatically reduces GC memory
usage peaks after layout tree churn and makes it easier for memory use
to fall back after large document updates.
Update layout factories, tree traversal, SVG layout node creation,
paintable back-pointers, and pseudo-element layout links to use RefPtr
ownership.
Make display: contents follow the same shape as Blink and WebKit: the
element itself does not create a layout node, and its children are
flattened into the nearest layout parent. Wrap direct non-whitespace
text in an anonymous inline node when the boxless element contributes
inherited style to that text.
Use an internal inline wrapper for display: contents pseudo-elements
so generated content can still participate in layout, painting, hit
testing, and pseudo-element queries. Keep CSSOM reporting the computed
display value from the pseudo style, not the internal wrapper.
Remove the retained out-of-tree layout node list and its testing hook,
since the flattened model does not need a side owner for boxless
elements. Add coverage for inherited text style, dynamic insertion
order, pseudo-element hit testing, and computed style queries.
Move ComputedProperties and CascadedProperties out of the GC. They no
longer contain strong references to GC-managed data.
Keep computed styles alive from DOM elements and animation updates with
RefPtr. Pass style into layout constructors by reference, since layout
only copies the values it needs while building nodes.
Use GC::Weak for cascade source links, so entries no longer keep the
style declaration or shadow root alive.
This isn't strictly correct as it stands currently, since the size
attribute isn't supposed to affect type="time" and others, but those
types currently end up with zero width instead.
Size could probably be applied through shadow DOM style, and the input
layout box would simply allow content sizing.
Use the text-control auto content size when calculating max-content
width for primitive text input widgets. CSS Sizing treats cyclic
percentage preferred sizes as initial values for non-replaced
max-content contributions, so an `appearance: none` input with
`width: 100%` should contribute its `width: auto` size instead of
collapsing to zero.
Keep the min-content path unchanged so the percentage-sized replaced
element rule can still compress non-button-like input controls for
flex automatic minimum sizing. Add coverage for an inline-flex
control matching the GitHub file search layout.
