These changes allow a minimal set of checks for font-src
CSP checks to pass.
Part of #4577
Part of #35035
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Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>
Adds support for both the content and the IDL attribute.
Note this doesn't cover dynamic updates to `document.styleSheets` and
the owner node of the sheet.
Testing: Covered by WPT
Fixes: #26739
Signed-off-by: Oriol Brufau <obrufau@igalia.com>