GitLab

Make a separate install source for installing from "Create Shortcut"
instead of sharing the same install source with install from menu.
Also record the Webapp.Install.InstallEvent for this source.

Bug: 1131210
Change-Id: Id0531e6d283603da01c02ba3c94cfa44138daacc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2439425
Commit-Queue: Phillis Tang <phillis@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812594}