Update rust-cssparser to 0.20.2.
This reduces memory consumption of list-valued properties in the common case of one entry in the list.
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TEST: fix and add case of po-observe.any.js
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1. implementing step 3 from the [`PerformanceObserver.observe()`](https://w3c.github.io/performance-timeline/#dom-performanceobserver-observe()) method spec properly.
2. also add cases about step 1 & 2
work on the top of #18283
r? @ferjm
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style: remove selector_map::find_push.
It has a single caller and is overly generic, which is going to make harder to
add fallible allocations to it.
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"javascript:" urls: execute in correct global scope
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#### Summary
This pull request makes `javascript:` urls execute in the correct global scope.
#### Example
```html
<script> var x = 4; </script>
<!-- this branch: logs "4" -->
<!-- master: undefined variable error -->
<a href="javascript:console.log(x)">link</a>
```
#### Questions
I'm new to servo and rust, so I'm unsure about these changes. In particular:
* What's the appropriate place to evaluate the js?
* I moved it to `handle_navigate`, but I'm not sure if this will catch all occurrences of `javascript:` urls. I also don't know if this will execute in the correct thread and the correct window.
* What should I do with the result of the js evaluation?
* I just ignored it. The previous behavior displayed it as the content of a new page load.
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A single transition value that includes 'none' for transition-property is
valid, so we should store whole specified values (if it's valid). Whereas,
the spec [1] clearly says for the case where there are multiple entries;
If there is more than one <single-transition> in the shorthand, and any of
the transitions has none as the <single-transition-property>, then the
declaration is invalid.
'none 2s linear 2s' is a test case for the former, '1s width, 2s none' is a
test case for the latter.
Note that with this patch, 'transition: none' is serialized as 'none 0s ease 0s'
instead of 'none' but it matches Gecko.
[1] https://drafts.csswg.org/css-transitions/#single-transition
MozReview-Commit-ID: 3o3z5GFyMqh
An observer disconnected after a mark must receive the mark
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I worked on top of #18283 as suggested [here](https://github.com/servo/servo/issues/18284#issuecomment-326043873).
r? @ferjm
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