Add gradient border support.
webrender add gradient border support in https://github.com/servo/webrender/pull/953. This pr add support in servo.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
<!-- Either: -->
- [X] These changes do not require tests because it should be covered by wpt
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15905)
<!-- Reviewable:end -->
remove unused `use` statements in mako helpers
These are no longer needed, according to `./mach build -d` and grep.
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because compilation is sufficient
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16121)
<!-- Reviewable:end -->
It should be checking the value of the 'writing-mode' property, not the value of
the "writing mode" concept. The latter is influenced by other properties like
'direction' and whatnot. That was causing this code to convert inlines to
inline-blocks if they just had a different direction from their parent, which is
not correct
stylo: Bug 1349834 - Update RESTYLE_STYLE_ATTRIBUTE to sync Gecko change.
This is an interdependent patch for Bug 1349834. We remove eRestyle_SVGAttrAnimations from nsRestyleHint, so need to update the bindgen and the value of RESTYLE_STYLE_ATTRIBUTE.
---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1349834](https://bugzilla.mozilla.org/show_bug.cgi?id=1349834)
- [X] These changes do not require tests because we just remove an unused flag from Gecko.
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16119)
<!-- Reviewable:end -->
Make writing-mode affect computed display
<!-- Please describe your changes on the following line: -->
The first manual test-case in #15754 passes now, but the second test-case still renders "Text" horizontally, which is apparently because of servo's experimental support for writing-mode.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#15754 (github issue number if applicable).
<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16044)
<!-- Reviewable:end -->
A new function, cascade_with_rules, takes StrongRuleNode
and computes cascading result values with the StrongRuleNode.
This new function will be used for getting after-change-style
for CSS Transitions.
Parsing / serialization for CSS contain
Adds parsing / serialization for CSS contain to the style package.
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#15955
- [x] There are tests for these changes
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15972)
<!-- Reviewable:end -->
