layout: use `au` in `HoistedSharedFragment`

Test results for linux-wpt-layout-2020 from try job (#9094771952):

Flaky unexpected result (13)

TIMEOUT [expected OK] /_webgl/conformance/glsl/misc/shader-uniform-packing-restrictions.html (#28103)
OK /css/css-fonts/variations/at-font-face-font-matching.html (#20684)
- PASS [expected FAIL] subtest: Matching font-weight: '430' should prefer '500' over '400 425'
- PASS [expected FAIL] subtest: Matching font-style: 'oblique 21deg' should prefer 'oblique 30deg 60deg' over 'oblique 40deg 50deg'
- PASS [expected FAIL] subtest: Matching font-style: 'oblique -10deg' should prefer 'oblique 0deg 10deg' over 'oblique 40deg 50deg'
- PASS [expected FAIL] subtest: Matching font-style: 'oblique -21deg' should prefer 'oblique -21deg' over 'oblique -60deg -40deg'
- PASS [expected FAIL] subtest: Matching font-style: 'oblique -21deg' should prefer 'oblique 0deg' over 'oblique 30deg 60deg'
- PASS [expected FAIL] subtest: Matching font-style: 'oblique -21deg' should prefer 'oblique 30deg 60deg' over 'oblique 40deg 50deg'
TIMEOUT /css/cssom-view/MediaQueryList-extends-EventTarget.html (#25269)
- TIMEOUT [expected PASS] subtest: listeners for "change" type are called
```
Test timed out
```
- NOTRUN [expected PASS] subtest: listeners with different type are not called
- NOTRUN [expected TIMEOUT] subtest: addEventListener "once" option is respected
OK /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/load-pageshow-events-window-open.html (#28691)
- PASS [expected FAIL] subtest: load event does not fire on window.open('about:blank')
OK /html/browsers/history/the-history-interface/traverse_the_history_2.html (#21383)
- PASS [expected FAIL] subtest: Multiple history traversals, last would be aborted
TIMEOUT [expected PASS] /html/canvas/element/manual/drawing-text-to-the-canvas/canvas.2d.disconnected-font-size-math.html (#30063)
TIMEOUT [expected OK] /html/interaction/focus/the-autofocus-attribute/autofocus-dialog.html (#29087)
- TIMEOUT [expected FAIL] subtest: <dialog>-contained autofocus element gets focused when the dialog is shown
```
Test timed out
```
CRASH [expected TIMEOUT] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_nonescaping-2.html (#22154)
OK [expected TIMEOUT] /html/semantics/forms/form-submission-0/reparent-form-during-planned-navigation-task.html (#29724)
- PASS [expected TIMEOUT] subtest: reparent-form-during-planned-navigation-task
OK /html/semantics/forms/form-submission-0/text-plain.window.html (#28687)
- PASS [expected FAIL] subtest: text/plain: 0x00 in value (formdata event)
TIMEOUT [expected OK] /resource-timing/nested-context-navigations-iframe.html (#24311)
- TIMEOUT [expected PASS] subtest: Test that crossorigin iframe navigations are not observable by the parent, even after history navigations by the parent
```
Test timed out
```
- NOTRUN [expected PASS] subtest: Test that cross-site iframe navigations are not observable by the parent, even after history navigations by the parent
- NOTRUN [expected PASS] subtest: Test that iframe navigations are not observable by the parent
- NOTRUN [expected PASS] subtest: Test that crossorigin iframe navigations are not observable by the parent
- NOTRUN [expected PASS] subtest: Test that cross-site iframe navigations are not observable by the parent
- NOTRUN [expected PASS] subtest: Test that iframe refreshes are not observable by the parent
- NOTRUN [expected PASS] subtest: Test that crossorigin iframe refreshes are not observable by the parent
- NOTRUN [expected PASS] subtest: Test that cross-site iframe refreshes are not observable by the parent
TIMEOUT /resource-timing/test_resource_timing.https.html (#25216)
- FAIL [expected PASS] subtest: PerformanceEntry has correct name, initiatorType, startTime, and duration (img)
```
assert_equals: expected 9879040 but got 9878784
```
TIMEOUT [expected OK] /webmessaging/without-ports/018.html (#24485)
- TIMEOUT [expected PASS] subtest: origin of the script that invoked the method, javascript:
```
Test timed out
```

Stable unexpected results that are known to be intermittent (12)

FAIL [expected PASS] /_mozilla/css/dirty_viewport.html (#13731)
FAIL [expected PASS] /_mozilla/css/iframe/hide_and_show.html (#15265)
FAIL [expected PASS] /_mozilla/gfx-rs-gecko/descriptor-ranges.html (#23258)
OK /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/iframe-src-aboutblank-navigate-immediately.html (#29048)
- PASS [expected FAIL] subtest: Navigating to a different document with link click
OK /html/browsers/history/the-history-interface/traverse_the_history_4.html (#21383)
- FAIL [expected PASS] subtest: Multiple history traversals, last would be aborted
```
assert_array_equals: Pages opened during history navigation expected property 1 to be 5 but got 3 (expected array [6, 5] got [6, 3])
```
OK [expected TIMEOUT] /html/infrastructure/urls/base-url/document-base-url-window-initiator-is-not-opener.https.window.html (#30970)
TIMEOUT [expected OK] /html/interaction/focus/the-autofocus-attribute/supported-elements.html (#24145)
- TIMEOUT [expected FAIL] subtest: Element with tabindex should support autofocus
```
Test timed out
```
- NOTRUN [expected PASS] subtest: Non-HTMLElement should not support autofocus
- NOTRUN [expected FAIL] subtest: Host element with delegatesFocus should support autofocus
- NOTRUN [expected FAIL] subtest: Host element with delegatesFocus including no focusable descendants should be skipped
- NOTRUN [expected FAIL] subtest: Area element should support autofocus
TIMEOUT [expected CRASH] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_escaping-2.html (#22667)
CRASH [expected OK] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_escaping-3.html (#24057)
CRASH [expected OK] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_nonescaping-1.html (#24066)
OK [expected TIMEOUT] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_nonescaping-3.html (#24066)
OK [expected TIMEOUT] /html/semantics/embedded-content/the-iframe-element/sandbox-top-navigation-user-activation-sticky.tentative.sub.window.html (#32154)
- FAIL [expected TIMEOUT] subtest: Allow top with user activation + user activation
```
promise_test: Unhandled rejection with value: object "TypeError: element.scrollIntoView is not a function"
```

Test results for linux-wpt-layout-2013 from try job (#9094771952):

Flaky unexpected result (9)

CRASH [expected PASS] /_webgl/conformance/glsl/bugs/nested-functions-should-not-crash.html (#30680)
TIMEOUT [expected PASS] /css/css-color/animation/opacity-animation-ending-correctly-002.html (#29216)
OK /css/cssom-view/MediaQueryList-addListener-handleEvent.html (#24571)
- FAIL [expected PASS] subtest: looks up handleEvent method on every event dispatch
```
assert_equals: expected 2 but got 1
```
OK /css/cssom-view/MediaQueryList-change-event-matches-value.html (#27973)
- FAIL [expected PASS] subtest: MediaQueryList.changed is correct for all lists in the document even during a change event handler
```
assert_equals: Should've fired the change event in both MediaQueryLists expected 2 but got 0
```
CRASH [expected OK] /html/canvas/offscreen/canvas-host/2d.canvas.host.size.attributes.parse.minus.html
OK /html/semantics/forms/form-submission-0/form-submit-iframe-then-location-navigate.html (#29634)
- FAIL [expected PASS] subtest: Verifies that location navigations take precedence when following form submissions.
```
assert_equals: expected "/html/semantics/forms/form-submission-0/resources/location.html" but got "/html/semantics/forms/form-submission-0/resources/form.html"
```
TIMEOUT [expected OK] /webmessaging/without-ports/018.html (#24485)
- TIMEOUT [expected PASS] subtest: origin of the script that invoked the method, javascript:
```
Test timed out
```
OK [expected ERROR] /workers/constructors/Worker/Worker-constructor.html (#22991)
OK /xhr/xhr-timeout-longtask.any.worker.html (#27663)
- FAIL [expected PASS] subtest: Long tasks should not trigger load timeout
```
assert_unreached: [object ProgressEvent] Reached unreachable code
```

Stable unexpected results that are known to be intermittent (12)

FAIL [expected PASS] /_mozilla/gfx-rs-gecko/descriptor-ranges.html (#23258)
OK [expected TIMEOUT] /custom-elements/reactions/customized-builtins/HTMLMediaElement.html (#31014)
TIMEOUT [expected OK] /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/iframe-src-aboutblank-navigate-immediately.html (#29048)
- TIMEOUT [expected FAIL] subtest: Navigating to a different document with link click
```
Test timed out
```
- NOTRUN [expected FAIL] subtest: Navigating to a different document with form submission
OK /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/load-pageshow-events-iframe-contentWindow.html (#28681)
- FAIL [expected PASS] subtest: load & pageshow events do not fire on contentWindow of <iframe> element created with src=''
```
assert_unreached: load should not be fired Reached unreachable code
```
OK /html/browsers/history/the-history-interface/traverse_the_history_4.html (#21383)
- PASS [expected FAIL] subtest: Multiple history traversals, last would be aborted
CRASH [expected OK] /html/browsers/windows/embedded-opener-remove-frame.html (#23867)
TIMEOUT [expected OK] /html/interaction/focus/the-autofocus-attribute/autofocus-dialog.html (#29087)
- TIMEOUT [expected FAIL] subtest: <dialog>-contained autofocus element gets focused when the dialog is shown
```
Test timed out
```
TIMEOUT [expected OK] /html/interaction/focus/the-autofocus-attribute/supported-elements.html (#24145)
- TIMEOUT [expected FAIL] subtest: Element with tabindex should support autofocus
```
Test timed out
```
- NOTRUN [expected PASS] subtest: Non-HTMLElement should not support autofocus
- NOTRUN [expected FAIL] subtest: Host element with delegatesFocus should support autofocus
- NOTRUN [expected FAIL] subtest: Host element with delegatesFocus including no focusable descendants should be skipped
- NOTRUN [expected FAIL] subtest: Area element should support autofocus
TIMEOUT [expected OK] /html/semantics/embedded-content/media-elements/track/track-element/no-cuechange-before-play.html (#31014)
- TIMEOUT [expected FAIL] subtest: Ensure that the 'cuechange' event is not fired before video playback has begun.
```
Test timed out
```
OK [expected CRASH] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_escaping-1.html (#22647)
TIMEOUT [expected OK] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_escaping-2.html (#22667)
TIMEOUT /resource-timing/test_resource_timing.https.html (#25216)
- PASS [expected FAIL] subtest: PerformanceEntry has correct name, initiatorType, startTime, and duration (img)

servo / servo

layout: use `au` in `HoistedSharedFragment` #32288