1191000 - Add some reftests to verify that "contain:layout" prevents flex item auto-sizing behavior

Status: NEW

(Core :: Layout, defect)

Description

[Daniel Holbert [:dholbert]]

Flex items have several default sizing-to-content behaviors - in particular:

 (1) "min-width:auto" ("min-height:auto") prevent flex items from shrinking below their intrinsic minimum width (height). [even if they have a smaller flex-basis value (or even if the flex container is shrinking them]

 (2) "flex-basis:auto;" combined with "width:auto" ("height:auto") give flex items a flex base size (a place to start their growing/shrinking) of the intrinsic preferred width.*

Both of these things depend on the contents of the flex item.

We should add tests to ensure that "contain: layout" breaks the dependency on the flex item's contents in these cases.

(Above, I'm focusing on row-oriented flex containers, for simplicity. Parentheticals refer to column-oriented flex containers. We should test both.)

* ("flex-basis: content" will expose the same "flex-basis:auto; width:auto" behavior more compactly, though we haven't implemented that keyword yet; bug 1105111)