arc: Added a comment to explain why we shutdown ARC session

BUG=b/149874690
TEST=None

Change-Id: I8390efa1df473a1c3a79726c01b75498aeaab989
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2087958
Commit-Queue: Muhammad Hasan Khan <mhasank@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Auto-Submit: Muhammad Hasan Khan <mhasank@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748866}

chrome/browser/chromeos/arc/session/arc_session_manager.cc

@@ -461,6 +461,10 @@ void ArcSessionManager::OnProvisioningFinished(ProvisioningResult result) {
       break;
   }
 
+  // When ARC provisioning fails due to Chrome failing to talk to server, we
+  // don't need to keep the ARC session running as the logs necessary to
+  // investigate are already present. ARC session will not provide any useful
+  // context.
   if (result == ProvisioningResult::ARC_STOPPED ||
       result == ProvisioningResult::CHROME_SERVER_COMMUNICATION_ERROR) {
     if (profile_->GetPrefs()->HasPrefPath(prefs::kArcSignedIn))