GitLab

This is in preparation for removing all traces of "gradient" from the
implementation.

No functional change; only file/class renames.

BUG=none
TEST=none

Change-Id: Ie2d0a16239c37557ea05a7c1eeea3180ad793980
Reviewed-on: https://chromium-review.googlesource.com/996714Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548503}