Signin/OAuth: Create an AccessTokenFetcher helper class

components/signin/core/browser/access_token_fetcher.h

Index: components/signin/core/browser/access_token_fetcher.h
diff --git a/components/signin/core/browser/access_token_fetcher.h b/components/signin/core/browser/access_token_fetcher.h
new file mode 100644
index 0000000000000000000000000000000000000000..a054bce7e64d3120156c01f4ad1bbfc2ce4c7e7a
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+++ b/components/signin/core/browser/access_token_fetcher.h
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+// Copyright 2017 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 COMPONENTS_SIGNIN_CORE_BROWSER_ACCESS_TOKEN_FETCHER_H_
+#define COMPONENTS_SIGNIN_CORE_BROWSER_ACCESS_TOKEN_FETCHER_H_
+
+#include <memory>
+#include <string>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "components/signin/core/browser/signin_manager_base.h"
+#include "google_apis/gaia/oauth2_token_service.h"
+
+// Helper class to ease the task of obtaining an OAuth2 access token. This
+// handles various special cases, e.g. when the refresh token isn't loaded yet
+// (during startup).
+// May only be used on the UI thread.
+class AccessTokenFetcher : public SigninManagerBase::Observer,
+                           public OAuth2TokenService::Observer,
+                           public OAuth2TokenService::Consumer {
+ public:
+  using TokenCallback = base::Callback<void(const std::string&)>;
+
+  // Instantiates a fetcher and immediately starts the process of obtaining an
+  // OAuth2 access token for the given |scopes|. The |callback| will be called
+  // with the access token on success, or with an empty string on failure. If
+  // the AccessTokenFetcher is destroyed before the process completes, the
+  // callback will not be called.
+  AccessTokenFetcher(const std::string& oauth_consumer_name,
+                     SigninManagerBase* signin_manager,
+                     OAuth2TokenService* token_service,
+                     const OAuth2TokenService::ScopeSet& scopes,
+                     const TokenCallback& callback);
+
+  ~AccessTokenFetcher() override;
+
+ private:
+  void Start();
+
+  void RunCallbackNotSignedIn();
+  void WaitForRefreshToken();
+  void StartAccessTokenRequest();
+
+  // SigninManagerBase::Observer implementation.
+  void GoogleSigninSucceeded(const std::string& account_id,
+                             const std::string& username,
+                             const std::string& password) override;
+  void GoogleSigninFailed(const GoogleServiceAuthError& error) override;
+
+  // OAuth2TokenService::Observer implementation.
+  void OnRefreshTokenAvailable(const std::string& account_id) override;
+  void OnRefreshTokensLoaded() override;
+
+  // OAuth2TokenService::Consumer implementation.
+  void OnGetTokenSuccess(const OAuth2TokenService::Request* request,
+                         const std::string& access_token,
+                         const base::Time& expiration_time) override;
+  void OnGetTokenFailure(const OAuth2TokenService::Request* request,
+                         const GoogleServiceAuthError& error) override;
+
+  SigninManagerBase* signin_manager_;
+  OAuth2TokenService* token_service_;
+  OAuth2TokenService::ScopeSet scopes_;
+
+  TokenCallback callback_;
+
+  bool waiting_for_sign_in_;
+  bool waiting_for_refresh_token_;
+
+  std::unique_ptr<OAuth2TokenService::Request> access_token_request_;
+
+  // When a token request gets canceled, we want to retry once.
+  bool access_token_retried_;
+
+  base::WeakPtrFactory<AccessTokenFetcher> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(AccessTokenFetcher);
+};
+
+#endif  // COMPONENTS_SIGNIN_CORE_BROWSER_ACCESS_TOKEN_FETCHER_H_