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* Update the character limit.
* Add the promotion text, which will be shown just below the app title
  on App Store. For example:
  https://drive.google.com/file/d/1dpHERWFhUkv7LSs-Mqxq7HmizDxMNiCV/view?usp=sharing

Bug: 756208
Change-Id: Ic8d6b23d2c292772c9ad7b5d928d3cb000ed98b4
Reviewed-on: https://chromium-review.googlesource.com/905504
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534863}