Have ExtensionApps not publish the Play Store app

That app is already published by the ArcApps app publisher, and having
two apps with different app_type's but the same app_id violates the App
Service programming model.

Also strengthen the AppUpdate::Merge check for this inconsistency.
Previously, it DCHECK'ed. Now, it LOG's and then DCHECK's, which is
more noisy when DCHECK's are no-ops.

BUG=826982

Change-Id: Ic413c89a32e45c2521b3a8ac28f05b9f86db64d9
Reviewed-on: https://chromium-review.googlesource.com/c/1420512
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625049}
5 files changed