Script thread creating layout thread should use the incomplete loads
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When a script thread creates a new layout thread, it does so by sending a message to an existing layout thread asking it to spawn. At the moment, we're only looking at the completed loads for that layout thread, so we can get a panic if two loads happen in quick succession. The temporary fix is to look for the layout thread in the incomplete loads too.
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The change to the unit test is necessary because the resource thread is not
resilient against either of these Senders being dropped while the resource
thread is running. Before this change, it held clones of those senders itself
(public_setup_chan_clone, private_setup_chan_clone).
Also remove now-dead code that rustc warns about.
It turns out that we lost support for some of our custom URL schemes; I intend
to reimplement them, but I believe this will be significantly easier to do
once the legacy code is out of the way.
script: Fix the scroll to top behavior
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When finding the indicated fragment, do not use the document element to indicate
the top of the Document, and when scrolling to the frament and we do not find a
element, scrolling the top if the fragment is empty or equal to "top".
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This also changes the algorithm to match w3c/csswg-drafts#754 instead of
the current cssom draft, because that makes the code simpler and matches
implementation of other browsers.
Implement access to CSSStyleRule for stylo
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This is the servo part of [bug 1307357](https://bugzilla.mozilla.org/show_bug.cgi?id=1307357) which has been reviewed by @heycam, @Manishearth and @SimonSapin.
r? @heycam
(`./mach test-tidy` reports several issues on bindings.rs... which I don't think is introduced by my patch... so I have no idea what to do here...)
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