stylo: Propagate quirks mode information from Gecko to Servo
r=bholley in bugzilla
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We need another flag that represents allow-negative-number for SMIL, so
this enum will also comprise the another parsing mode that allows negative number.
Servo-side change stylesheet_set entry unique_id to u64
https://bugzilla.mozilla.org/show_bug.cgi?id=1363572https://reviewboard.mozilla.org/r/138092/
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Allow stylo to do lazier stylist rebuilds
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