[css-layout-api] LayoutClass should probably have a `measure` callback

[upsuper]

In the current draft, there is a layout callback function in LayoutClass, which returns LayoutResult includes minContent and maxContent as well as width and height.

I don't think this setting makes much sense. I believe the minContent and maxContent are values used by parent to decide a proper inline-axis length of its child. If the width and height has been decided by the child, having minContent and maxContent doesn't give the parent something really useful.

I'd suggest we have an additional measure callback, which takes the same parameters as the current layout, and returns a struct only includes minContent and maxContent. Then its parent decides geometry for the the box and calls layout with something like "suggested size". The Box interface would need to be adjusted accordingly as well.

I believe this is basically how Android's layout process work.

[bfgeek]

This has now appeared as the intrinsicSizes callback in the current specification.