Replace --add-to-shelf flag with kAppBanners feature.

The add to shelf flag was poorly named and doesn't use the new feature
goodness.

With this change, functionality dependent on the kBookmarkApps flag is
also enabled if the kAppBanners flag is enabled.

BUG=734897

Review-Url: https://codereview.chromium.org/2944283002
Cr-Commit-Position: refs/heads/master@{#482889}
12 files changed