Show reason in logs when crostini is not allowed

(cherry picked from commit ebaed9a)

Change-Id: I975d1b0af0f2824314b38fdb37ad9bdaaa2d81e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2741878
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Jason Lin <lxj@google.com>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#860617}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2738579
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/4430@{#214}
Cr-Branched-From: e5ce7dc-refs/heads/master@{#857950}

chrome/browser/chromeos/crostini/crostini_util.cc

@@ -387,7 +387,9 @@ void LaunchCrostiniApp(Profile* profile,
                        const std::vector<LaunchArg>& args,
                        CrostiniSuccessCallback callback) {
   // Policies can change under us, and crostini may now be forbidden.
-  if (!CrostiniFeatures::Get()->IsAllowedNow(profile)) {
+  std::string reason;
+  if (!CrostiniFeatures::Get()->IsAllowedNow(profile, &reason)) {
+    LOG(ERROR) << "Crostini not allowed: " << reason;
     return std::move(callback).Run(false, "Crostini UI not allowed");
   }
   auto* crostini_manager = crostini::CrostiniManager::GetForProfile(profile);