GitLab

ActivityViewModel has the necessary information that should be displayed to the
user. So provide mechanism for it to be able to update the view when the relevant
information (e.g. title, icon, color) changes.

BUG=none
R=oshima@chromium.org

Review URL: https://codereview.chromium.org/694413005

Cr-Commit-Position: refs/heads/master@{#302753}