GitLab

This CL adds TutorialManager class to the video tutorials. Also
cleaned up a few methods on the storage layer.

Bug: 1130260
Change-Id: Ida331aefc538daddccd30175cd5652152cf4ab4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2420779
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809192}