Merge anonymous flex item siblings.

When we detach a flex item, we might end up with anonymous flex item
in-flow siblings which should be merged into a single flex item because
their text children makes up a contiguous run of text.

The case where a flex item goes from in-flow to absolute positioned is
not fixed by this CL. That is the reason for the failing sub-test.

Bug: 788379, 657748
Change-Id: Idf0bee2b490982b9bc987d31ceccf894a64147f8
Reviewed-on: https://chromium-review.googlesource.com/795724
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520501}
10 files changed