Bugzilla

Here's a testcase to illustrate why we can't just leave `mainAxisCoord` untouched as noted in my [inline comment](https://phabricator.services.mozilla.com/D86633#inline-513388) in phabricator.

This is a variant of the existing web-platform test https://searchfox.org/mozilla-central/source/testing/web-platform/tests/css/css-sizing/aspect-ratio/flex-aspect-ratio-001.tentative.html -- I've moved the test's styles to a `<style>` block, and added my own tweaks in inline styles.

With your current first patch in the patch stack here, the third chunk  in this testcase renders as a skinny green bar, rather than a green square. But really, all three chunks *should* render the same. (Chrome "agrees" with us right now simply because they don't support the explicit `content` keyword for `flex-basis`, so they're not a trustworthy source on the rendering of this third example)

Here's a testcase to illustrate why we can't just leave `mainAxisCoord` untouched as noted in my [inline comment](https://phabricator.services.mozilla.com/D86633#inline-513388) in phabricator.

This is a variant of the existing web-platform test https://searchfox.org/mozilla-central/source/testing/web-platform/tests/css/css-sizing/aspect-ratio/flex-aspect-ratio-001.tentative.html -- I've moved the test's styles to a `<style>` block, and added my own tweaks in inline styles.

With your current first patch in the patch stack here, the third chunk  in this testcase renders as a skinny green bar, rather than a green square. But really, all three chunks *should* render the same. (Chrome "agrees" with us right now simply because they [don't support the explicit `content` keyword for `flex-basis`](https://bugs.chromium.org/p/chromium/issues/detail?id=470421), so they're not a trustworthy source on the rendering of this third example)