First draft of an App Service Crostini publisher

Lots of TODOs, but there's enough implemented so that running "chrome
--enable-features=AppServiceAsh" will populate the launcher with
Crostini apps' names and icons, and clicking on the icon will launch the
app.

BUG=826982

Change-Id: I5c23abb8248f7025393deddba1abea79b97d3510
Reviewed-on: https://chromium-review.googlesource.com/c/1445172
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627872}
10 files changed