Don't display update prompt for non-update alerts.

Previously, if the alert severity was anything other than NONE, the
tooltip on the app menu prompted the user that an upgrade was available.
But alerts are used for other things too (like an extension that has
been disabled) so now we display a generic alert tooltip for non-upgrade
situations.

Bug: 889779
Change-Id: I952bc7803d09fbd7076b4c0636eb619085aee689
Reviewed-on: https://chromium-review.googlesource.com/c/1431475
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Commit-Queue: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625408}
3 files changed