getComputedStyle doesn't absolutize percentages in sticky positioning

[Oriol Brufau]

Run this code for some element that generates boxes:

```js
element.style.position = "-webkit-sticky";
element.style.top = "10%";
getComputedStyle(element).top;
```

Actual value: "10%"
Expected: the percentage should be absolutized into a length

[Emilio Cobos Álvarez (:emilio)]

Beware of other browsers not being interoperable here, see: https://github.com/w3c/csswg-drafts/issues/3115

[Joonghun Park]

* Corresponding blink bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=884544

[Joonghun Park]

Created attachment 368906 [details]
Patch

[Joonghun Park]

Hi, Could this change be reviewed?

[EWS Watchlist]

Comment on attachment 368906 [details]
Patch

Attachment 368906 [details] did not pass win-ews (win):
Output: https://webkit-queues.webkit.org/results/12080674

New failing tests:
legacy-animation-engine/fast/layers/no-clipping-overflow-hidden-hardware-acceleration.html

[EWS Watchlist]

Created attachment 368912 [details]
Archive of layout-test-results from ews215 for win-future

The attached test failures were seen while running run-webkit-tests on the win-ews.
Bot: ews215  Port: win-future  Platform: CYGWIN_NT-10.0-17763-3.0.5-338.x86_64-x86_64-64bit

[Joonghun Park]

It seems that win-ews is unstable currently seeing https://webkit-queues.webkit.org/queue-status/win-ews.

So the win-ews's failure result could be ignored I guess.

[Antti Koivisto]

Comment on attachment 368906 [details]
Patch

r=me

[WebKit Commit Bot]

Comment on attachment 368906 [details]
Patch

Clearing flags on attachment: 368906

Committed r244906: <https://trac.webkit.org/changeset/244906>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/50442414>