Fix race issue in ArcAuthService.

chrome/browser/chromeos/arc/auth/arc_auth_code_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_CODE_FETCHER_H_
+#define CHROME_BROWSER_CHROMEOS_ARC_AUTH_ARC_AUTH_CODE_FETCHER_H_
+
+#include <string>
+
+#include "base/callback.h"
+
+namespace arc {
+
+// Interface to implement auth_code fetching.
+class ArcAuthCodeFetcher {
+ public:
+  virtual ~ArcAuthCodeFetcher() = default;
+
+  // Fetches the |auth_code|. On success, |callback| is called with the
+  // fetched |auth_code|. Otherwise, |callback| is called with empty string.
+  // Fetch() should be called once par 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_code)>;
+  virtual void Fetch(const FetchCallback& callback) = 0;
+};
+
+}  // namespace arc
+
+#endif  // CHROME_BROWSER_CHROMEOS_ARC_AUTH_ARC_AUTH_CODE_FETCHER_H_