[Webkit-unassigned] [Bug 287638] New: Element with `overflow: scroll` does not correctly account for margins of its child to determine the scrollable area with `writing-mode: vertical-rl`

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=287638

            Bug ID: 287638
           Summary: Element with `overflow: scroll` does not correctly
                    account for margins of its child to determine the
                    scrollable area with `writing-mode: vertical-rl`
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: graouts at webkit.org
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Look at the attached test case which is this simple HTML and CSS:

```
<style>

#scroller {
    overflow: scroll;
    width: 80px;
    height: 100px;
    writing-mode: vertical-rl;
    background-color: gray;
}

#target {
    margin: 150px;
    width: 50px;
    height: 50px;
    background-color: green;
}

</style>

<div id=scroller>
    <div id=target></div>
</div>
```

In Chrome, `scroller.scrollHeight` returns `350` while in ToT as of 290337 at main it returns `200`, as if `margin` for the `#target` was `0` and not `150px`.

This affects imported/w3c/web-platform-tests/scroll-animations/css/view-timeline-inset-animation.html.

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