[layout] Make flex-basis accept the 'stretch' keyword
Only parser changes were necessary; length_utils already had the
necessary layout logic.
Change-Id: I3c23ac47c6ccebdbec07edf75ed83a6184172ad3
Bug: 41253915,353538495
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5985742
Reviewed-by: David Baron dbaron@chromium.org
Commit-Queue: David Grogan dgrogan@chromium.org
Cr-Commit-Position: refs/heads/main@{#1377766}