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This CL
1 - Changes Tutorial not to be a subclass of ImageTile.
2 - Handled additional feature type enum types.
3 - Added some unittests
4 - Fixed a CSS bug

Change-Id: Iceca0057f7e0d9b549af5481a12c7f1565e21441
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464855Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816693}