[layoutng] Inline the ShapeResultSpacing constructor

Good performance data:
https://pinpoint-dot-chromeperf.appspot.com/job/11a140e8f40000

Change-Id: I171ca316fbd8336576dbc78929bf48d35b1494e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1330077
Auto-Submit: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#640900}
2 files changed