Avoid stretching the parent of a column spanner.

Avoid stretching the parent of a column spanner.

We used to stretch the parent of a spanner, so that it would take up all
remaining space in the last column, to make sure that column content after the
spanner wouldn't bleed into the column preceding the spanner.

This stretching (a kludge, really) was problematic, especially if the parent
had fixed height, which would override the stretching. This would lead to
broken layout, and even assertion failures.

Instead, deal with the fact that the last column may be shorter than the
others. We don't want this for paged overflow, though, or it'd be impossible to
scroll the last page completely into view.

BUG=499706
R=dsinclair@chromium.org,jchaffraix@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197392

[dsinclair, 2015-06-18 19:57:58]

The CQ bit was checked by dsinclair@chromium.org

[dsinclair, 2015-06-18 19:57:58]

lgtm

[commit-bot: I haz the power, 2015-06-18 19:59:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1181483005/20001

[commit-bot: I haz the power, 2015-06-18 20:05:04]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197392