[LayoutNG] Remove return reference for NGConstraintSpaceBuilder methods.

From: https://chromium-review.googlesource.com/c/chromium/src/+/1752692

This removes return reference for NGConstraintSpaceBuilder methods.

Change-Id: I599dbee592397b3704de21779a7085378733e4a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1752287
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686803}
17 files changed