Refactor to send iframe resize messages directly from layout thread to constellation
<!-- Please describe your changes on the following line: -->
---
<!-- 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#14682.
<!-- Either: -->
r? @jdm
passing tests:
tests/wpt/mozilla/tests/css/matchMedia.html, tests/wpt/mozilla/tests/mozilla/window_resize_not_triggered_on_load.html, tests/wpt/mozilla/tests/mozilla/iframe/resize_after_load.html, tests/wpt/mozilla/tests/css/meta_viewport_resize.html
<!-- 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/15129)
<!-- Reviewable:end -->
Index the session past correctly when discarding.
<!-- Please describe your changes on the following line: -->
Oops, indexed from the wrong end when discarding documents in #14312.
---
<!-- 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 do not require tests because we're not testing document discarding
<!-- 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/14860)
<!-- Reviewable:end -->
Implement browsing context discarding
<!-- Please describe your changes on the following line: -->
Implement browsing context discarding (https://html.spec.whatwg.org/multipage/browsers.html#discard-a-document).
* When a pipeline is closed, inform the script thread whether the browsing context is to be discarded.
* In script threads, synchronously discard any similar-origin documents and browsing contexts.
* When a browsing context is discarded, it loses the reference to the active document, but the window keeps it, so we need to move the `Document` pointer from `BrowsingContext` to `Window`.
* Fix the webIDL for Window to make parent and top optional (the spec says they can return null when the browsing context is discarded).
---
<!-- 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#14411
- [X] There are tests for these changes
<!-- 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/14559)
<!-- Reviewable:end -->
Rename ScriptChan in constellation to EventLoop
<!-- Please describe your changes on the following line: -->
We currently have a type `ScriptChan` in the constellation, which is named after its implementation rather than its semantics. In the spec, the nearest concept seems to be event loop https://html.spec.whatwg.org/multipage/#event-loop.
---
<!-- 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 do not require tests because renaming.
<!-- 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/14260)
<!-- Reviewable:end -->
Reimplement scrolling to fragments
<!-- Please describe your changes on the following line: -->
---
<!-- 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#13736, #10753 (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. -->
This reimplemntation of the feature uses ScrollRootIds to scroll
particular scrollable areas of the page.
Fixes#13736.
Fixes#10753.
<!-- 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/14367)
<!-- Reviewable:end -->
Script thread with no root document
<!-- Please describe your changes on the following line: -->
This PR removes the single root document from the script thread, and replaces it by a lookup table from `PipelineId`s to `Document`s. This is needed if we're going to share script threads, as per #633.
The last commit is the one that matters, the ones before are #13646.
cc @jdm @Ms2ger @ConnorGBrewster
---
<!-- 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 do not require tests because refactoring
<!-- 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/14013)
<!-- Reviewable:end -->
Script lookup iframes by frameid
<!-- Please describe your changes on the following line: -->
Lookup iframes by `FrameId` rather than `PipelineId`. This should make lookup much more reliable, since the frame id doesn't change.
cc @ConnorGBrewster @aneeshusa
---
<!-- 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 do not require tests because refactoring
<!-- 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/13646)
<!-- Reviewable:end -->
Tidying up constellation.
<!-- Please describe your changes on the following line: -->
Some miscellaneous tidying up to the constellation:
- improve the efficiency of testing emptiness of the joint session past and future,
- add some helpful debug logs,
- make the if-statement for pipeline traversal easier to read.
r? @ConnorGBrewster
---
<!-- 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 do not require tests because tidying up
<!-- 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/13966)
<!-- Reviewable:end -->
Layers were a feature of the legacy drawing path. If we re-add them at
some point, it probably makes more sense to make them a product of
display list inspection.
This change also remove a bunch of dead painting code.
