GitLab

This CL:

* Makes the build target generate the credits page for the app.
* Adds the credits page to the help view.

Bug: 745233
Change-Id: Id612c7140fbdcc9433854d26f8c33509c28ac3c2
Reviewed-on: https://chromium-review.googlesource.com/575041Reviewed-by: Scott Nichols <nicholss@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487620}