GitLab

Creates shared unit test helpers for MockMetadata and MockGalleryItem
since these concepts are used in multiple unittest files. This means
updating the corresponding unittest.html files that are not yet auto-
generated.

Bug: 867700
Change-Id: Ia77bac5f9dc14abb1f92bb90a8c545d6998e0160
Reviewed-on: https://chromium-review.googlesource.com/1172170Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582746}