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This allows us to set a different value for the width in the new UI.

This mechanism is similar to what is already in use in ShelfConstants.

Bug: 880586, 880589
Change-Id: Ice307799331e4765a3b6bc289d3442e23bf90c4c
Reviewed-on: https://chromium-review.googlesource.com/1205751Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588833}