Treat indefinite percentages as auto offsets in relative positioning

[Loirooriol]

Instead of just resolving the percentages against zero.
The spec is not clear (w3c/csswg-drafts#9353), but this way we match Gecko, Blink and WebKit.

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• There are tests for these changes

[github-actions]

🔨 Triggering try run (#8133581508) for Linux WPT

[github-actions]

Test results for linux-wpt-layout-2020 from try job (#8133581508):

Flaky unexpected result (14)

• TIMEOUT [expected OK] /_webgl/conformance/glsl/misc/shader-with-non-reserved-words.html (#16216)
  • NOTRUN [expected PASS] subtest: Overall test
• TIMEOUT [expected OK] /_webgl/conformance/uniforms/out-of-bounds-uniform-array-access.html (#26225)
  • NOTRUN [expected PASS] subtest: Overall test
• OK /css/css-fonts/variations/at-font-face-font-matching.html (#20684)
  • PASS [expected FAIL] subtest: Matching font-weight: '430' should prefer '350 399' over '340 398'
  • PASS [expected FAIL] subtest: Matching font-weight: '430' should prefer '340 398' over '501 550'
  • PASS [expected FAIL] subtest: Matching font-weight: '500' should prefer '500' over '450 460'
  • PASS [expected FAIL] subtest: Matching font-stretch: '110%' should prefer '110% 120%' over '115% 116%'
  • PASS [expected FAIL] subtest: Matching font-style: 'normal' should prefer 'oblique 0deg' over 'oblique 10deg 40deg'
  • PASS [expected FAIL] subtest: Matching font-style: 'normal' should prefer 'oblique 20deg 30deg' over 'oblique -50deg -20deg'
  • PASS [expected FAIL] subtest: Matching font-style: 'normal' should prefer 'oblique -50deg -20deg' over 'oblique -40deg -30deg'
  • PASS [expected FAIL] subtest: Matching font-style: 'italic' should prefer 'italic' over 'oblique 20deg'
  • PASS [expected FAIL] subtest: Matching font-style: 'oblique 21deg' should prefer 'oblique -50deg -20deg' over 'oblique -40deg -30deg'
  • PASS [expected FAIL] subtest: Matching font-style: 'oblique 10deg' should prefer 'oblique 10deg' over 'oblique 5deg'
  • And 2 more unexpected results...
• OK /css/cssom-view/matchMedia.html (#31428)
  • PASS [expected FAIL] subtest: iframe.matchMedia("(width: 200px)") matches
• TIMEOUT [expected OK] /custom-elements/reactions/customized-builtins/HTMLMediaElement.html (#31014)
• OK /html/browsers/browsing-the-web/navigating-across-documents/empty-iframe-load-event.html (#29066)
  • FAIL [expected PASS] subtest: Check execution order from nested timeout assert_equals: Expected nested setTimeout to run second expected true but got false
  • FAIL [expected PASS] subtest: Check execution order on load handler assert_equals: Expected onload to run first expected false but got true
• OK /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/load-pageshow-events-window-open.html (#28691)
  • FAIL [expected PASS] subtest: load event does not fire on window.open('about:blank') assert_unreached: load should not be fired Reached unreachable code
• OK /html/browsers/browsing-the-web/navigating-across-documents/navigate-to-unparseable-url.html (#29050)
  • PASS [expected FAIL] subtest: <a> tag navigate fails for unparseable URLs
• 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_escaping-3.html (#24057)
• TIMEOUT /html/webappapis/scripting/events/compile-event-handler-settings-objects.html (#24246)
  • TIMEOUT [expected FAIL] subtest: The entry settings object while executing the compiled callback via Web IDL's invoke must be that of the node document Test timed out
• TIMEOUT [expected OK] /html/webappapis/scripting/processing-model-2/integration-with-the-javascript-job-queue/promise-job-entry-different-function-realm.html (#25805)
  • TIMEOUT [expected FAIL] subtest: Fulfillment handler on pending-then-fulfilled promise Test timed out
  • TIMEOUT [expected FAIL] subtest: Rejection handler on pending-then-rejected promise Test timed out
• OK [expected TIMEOUT] /webmessaging/without-ports/017.html (#24486)
  • PASS [expected TIMEOUT] subtest: origin of the script that invoked the method, about:blank
• OK [expected ERROR] /workers/constructors/Worker/Worker-constructor.html (#22991)

Stable unexpected results that are known to be intermittent (18)

• FAIL [expected PASS] /_mozilla/css/dirty_viewport.html (#13731)
• FAIL [expected PASS] /_mozilla/mozilla/iframe/resize_after_load.html (#13573)
• TIMEOUT [expected OK] /_webgl/conformance/glsl/misc/shader-uniform-packing-restrictions.html (#28103)
  • NOTRUN [expected PASS] subtest: Overall test
• 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 /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/load-pageshow-events-iframe-contentWindow.html (#28681)
  • PASS [expected FAIL] subtest: load & pageshow events do not fire on contentWindow of <iframe> element created with src='about:blank'
• OK [expected TIMEOUT] /html/browsers/browsing-the-web/navigating-across-documents/javascript-url-referrer.window.html (#29081)
  • PASS [expected TIMEOUT] subtest: no-referrer referrer policy used to create the starting page
• OK /html/browsers/history/the-history-interface/traverse_the_history_5.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])
• CRASH [expected PASS] /html/canvas/element/manual/drawing-text-to-the-canvas/canvas.2d.disconnected-font-size-math.html (#30063)
• TIMEOUT [expected OK] /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: Host element with delegatesFocus including no focusable descendants should be skipped Test timed out
  • NOTRUN [expected FAIL] subtest: Area element should support autofocus
• OK [expected TIMEOUT] /html/semantics/embedded-content/media-elements/track/track-element/no-cuechange-before-play.html (#31014)
  • FAIL [expected TIMEOUT] subtest: Ensure that the 'cuechange' event is not fired before video playback has begun. assert_true: Not expecting event, but got canplaythrough event expected true got false
• OK [expected TIMEOUT] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_escaping-2.html (#22667)
  • FAIL [expected TIMEOUT] subtest: Check that popups from a sandboxed iframe escape the sandbox if
    allow-popups-to-escape-sandbox is used assert_equals: It came from a sandboxed iframe expected "null" but got "http://web-platform.test:8000"
• CRASH [expected TIMEOUT] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_nonescaping-1.html (#24066)
• OK [expected ERROR] /html/semantics/scripting-1/the-script-element/defer-script/async-script.html?reload (#29054)
• OK [expected TIMEOUT] /resource-timing/nested-context-navigations-iframe.html (#24311)
  • PASS [expected TIMEOUT] subtest: Test that iframe refreshes are not observable by the parent
  • PASS [expected NOTRUN] subtest: Test that crossorigin iframe refreshes are not observable by the parent
  • PASS [expected NOTRUN] subtest: Test that cross-site iframe refreshes are not observable by the parent
• OK [expected TIMEOUT] /webmessaging/with-ports/018.html (#24485)
  • PASS [expected TIMEOUT] subtest: origin of the script that invoked the method, javascript:
• 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 /workers/WorkerGlobalScope-close.html (#23064)
  • FAIL [expected PASS] subtest: Test sending a message after closing. assert_not_equals: got disallowed value "pong"

Stable unexpected results (3)

• PASS [expected FAIL] /css/css-position/position-relative-007.html
• PASS [expected FAIL] /css/css-values/calc-offsets-relative-bottom-1.html
• PASS [expected FAIL] /css/css-values/calc-offsets-relative-top-1.html

[github-actions]

⚠️ Try run (#8133581508) failed.