Process css animations for gecko
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This is a PR for https://bugzilla.mozilla.org/show_bug.cgi?id=1341985 .
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Change the predefined type of flex-basis and make gecko glue auto-generate
Gecko [doesn't support](https://bugzilla.mozilla.org/show_bug.cgi?id=1105111) content value in flex-basis yet. We had to change the predefined type to `LengthOrPercentageOrAuto` in stylo build.
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We create the SequentialTask only if:
* We have no old computed values and we have animation name style in the new
computed values.
* Any animation properties is changed.
* display property is changed from 'none' and we have animation name style.
* display property is changed to 'none'.
In a subsequent patch we skip the SequentialTask if we have no running
animations and the display propery is changed to 'none'.
Stylo - gecko glue code for text-justify
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Implement gecko glue for text-justify property.
Gecko has supported text-justify in [Bug 276079](https://bugzilla.mozilla.org/show_bug.cgi?id=276079), and going to pref-on on Nightly very soon in [Bug 1343512](https://bugzilla.mozilla.org/show_bug.cgi?id=1343512). Let's make it work for stylo.
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Reject negative border radius
Replacerd Parse in parse_one_set_of_border_values with parse_non_negative and added tests for it
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Make text decoration testable and do not serialize initial text-decoration-style
Servo now uses the same name for the text-decoration-line longhand property as Gecko. This was done to enable testing of the text-decoration shorthand.
The text-decoration shorthand has been fixed to not serialize initial text-decoration-style.
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Deduplicate declarations on insertion, not at the end of parsing a block
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Servo side of gecko bug 1343078: update bindinggen bits for the changes I'm making to Gecko atoms.
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Otherwise they trigger their animations and transitions.
We will introduce gecko's own process in bug 1341985 (animations) and
bug 1341372 (transitions).
