Don't change the height of a layout object while not laying it out.

Don't change the height of a layout object while not laying it out.

The old flexbox implementation did that. This still used to work halfheartedly
by accident until the fix for bug 498770, though, because we used to mark
out-of-flow positioned children in updateBlockChildDirtyBitsBeforeLayout(). But
it never worked for anything other than direct children. Added one test for the
recent regression (out-of-flow child) and one test that has probably never
passed, until now (out-of-flow grandchild).

We need to be inside layout() when setting the height of an object, or we won't
be able to detect any changes and thus fail to relayout positioned descendants
that may be affected.

BUG=504239
R=leviw@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=198017

[leviw_travelin_and_unemployed, 2015-06-29 18:54:45]

Oof... I'm sorry you've now had to touch deprecated flexbox.

LGTM, sir.

[leviw_travelin_and_unemployed, 2015-06-29 18:54:50]

The CQ bit was checked by leviw@chromium.org

[commit-bot: I haz the power, 2015-06-29 18:55:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1213843002/20001

[commit-bot: I haz the power, 2015-06-29 20:22:18]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=198017