Check Crostini UI allowed before launching apps.

It is possible for Crostini apps to be disallowed by policy. This can change
at any time for a give machine, so we always need to check.

While the pinning bug is still happening, we also need this as a failsafe.

Bug: 881681
Change-Id: I2e2497ef9cdaee7f989d38931a88886d52535cf9
Reviewed-on: https://chromium-review.googlesource.com/1212373Reviewed-by: Timothy Loh <timloh@chromium.org>
Commit-Queue: Nicholas Verne <nverne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589441}

chrome/browser/chromeos/crostini/crostini_util.cc

@@ -266,6 +266,10 @@ void LaunchCrostiniApp(Profile* profile,
                        const std::string& app_id,
                        int64_t display_id,
                        const std::vector<std::string>& files) {
+  // Policies can change under us, and crostini may now be forbidden.
+  if (!IsCrostiniUIAllowedForProfile(profile)) {
+    return;
+  }
   auto* crostini_manager = crostini::CrostiniManager::GetForProfile(profile);
   crostini::CrostiniRegistryService* registry_service =
       crostini::CrostiniRegistryServiceFactory::GetForProfile(profile);