Show different error message if ARC is disabled.

chrome/browser/chromeos/arc/auth/arc_auth_info_fetcher.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_CHROMEOS_ARC_AUTH_ARC_AUTH_INFO_FETCHER_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_AUTH_ARC_AUTH_INFO_FETCHER_H_
 
 #include <string>
 
 #include "base/callback.h"
 
 namespace arc {
 
 // Interface to implement auth_code or enrollment token fetching.
 class ArcAuthInfoFetcher {
  public:
   virtual ~ArcAuthInfoFetcher() = default;
 
-  // Fetches the auth code or the enrollment token. On success, |callback| is
-  // called with the fetched |auth_info|. Otherwise, |callback| is called with
-  // empty string.
+  enum class Status {
+    SUCCESS,       // The fetch was successful.
+    FAILURE,       // The request failed.
+    ARC_DISABLED,  // ARC is not enabled.
+  };
+
+  // Fetches the auth code or the enrollment token.
+  // On success, |callback| is called with |status| = SUCCESS and with the
+  // fetched |auth_info|. Otherwise, |status| contains the reason of the
+  // failure.
   // Fetch() should be called once per instance, and it is expected that
   // the inflight operation is cancelled without calling the |callback|
   // when the instance is deleted.
-  using FetchCallback = base::Callback<void(const std::string& auth_info)>;
+  using FetchCallback =
+      base::Callback<void(Status status, const std::string& auth_info)>;
   virtual void Fetch(const FetchCallback& callback) = 0;
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_AUTH_ARC_AUTH_INFO_FETCHER_H_