GitLab

 - remove progress_center_item_group_unittest.html
 - add BUILD rules to auto-generate and compile the unittest
 - fix Closure compile errors

Bug: 910989
Change-Id: I1fc5c09f6d13026b21eee4717dc303ab8beb8ee5
Reviewed-on: https://chromium-review.googlesource.com/c/1356730
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613005}