GitLab

Change optimize_webui to generate a manifest file when an |out_manifest|
argument is provided.

Started from:
https://chromium-review.googlesource.com/c/chromium/src/+/2443211
by dpapad@

Bug: 1132403
Change-Id: Ia80c4d2c004ec4414c500c407e2d2c8d187ff847
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463962Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815777}