GitLab

Adds tests for:
* Clicking on "System security settings" button in EULA screen
* Accepting and rejecting usage stats collection
* Clicking on "Learn more" button in EULA screen

Removes dead code from EulaScreen class.

Adds a HelpApp extension manifest to use in tests and modifies
HelpAppLauncher class to allow tests to set the extension id.

Adds a HelpAppTestHelper class to facilitate writing tests that
open HelpApp dialogs.

Change-Id: Id7841be5bf3faabb067d3a75d3b034bdf0e00e32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1554123
Commit-Queue: Tony De Luna <tonydeluna@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648759}