Prevents observably calling Trusted Types, which can run arbitrary JS,
cause crashes due to use of MUST and allow arbitrary JS to modify
internal elements.
For attributes like Element.ariaControlsElements, which are a reflection
of FrozenArray<Element>, we must return the same JS::Array object every
time the attribute is invoked - until its contents have changed. This
patch implements caching of the reflected array in accordance with the
spec.
We are meant to store a weak reference to the element indicated by this
attribute, rather than a GC-protected strong reference. This also hoists
the "get the attr-associated element" AO into its own function, rather
than being hidden in IDL, to match "get the attr-associated elements".
There are ARIA attributes, e.g. ariaControlsElements, which refer to a
list of elements by their ID. For example:
<div aria-controls="item1 item2">
The div.ariaControlsElements attribute would be a list of elements whose
ID matches the values in the aria-controls attribute.
This change adds a virtual to_element function to ARIAMixin, and
overrides it in DOM::Element so it can then be used back inside
ARIAMixin to get an element when needed (for example, when computing a
role requires checking the roles of ancestors of an element).
This change separates the steps for checking the string value of the
ARIA “role” attribute out from the element.role_or_default() function
into a separate function — in order to expose a way to just check if the
ARIA “role” attribute actually has a value, without also then computing
a default role value if no “role” attribute value was found.
Otherwise, without this change, the only available function for
retrieving ARIA role values is the element.role_or_default() function —
which always does the additional step of computing (and returning) a
default role value if no “role” attribute is found.
We are currently constructing the attribute names as FlyStrings every
time we invoke one of the ARIA attributes getters/setters. If there are
not any other instances of these strings in-memory, then we're thrashing
the FlyString cache.
Instead, let's follow suit of all other Web attributes - use an x-macro
to generate the attribute names.
