[Chromoting] Add a helper class to map an OAuth access token to an email address.

remoting/host/gaia_user_email_fetcher.h

Index: remoting/host/gaia_user_email_fetcher.h
diff --git a/remoting/host/gaia_user_email_fetcher.h b/remoting/host/gaia_user_email_fetcher.h
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+// Copyright (c) 2012 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 REMOTING_HOST_GAIA_USER_EMAIL_FETCHER_H_
+#define REMOTING_HOST_GAIA_USER_EMAIL_FETCHER_H_
+
+#include <string>
+
+#include "base/memory/ref_counted.h"
+#include "base/message_loop_proxy.h"
+
+namespace net {
+class URLRequestContextGetter;
+}  // namespace net
+
+// A helper class to get a user's email, given an OAuth access token.
+// TODO(simonmorris): Consider moving this to google_apis/gaia.
+namespace remoting {
+
+class GaiaUserEmailFetcher {
+ public:
+  class Delegate {
+   public:
+    virtual ~Delegate() { }
+
+    // Invoked on a successful response to the GetUserEmail request.
+    virtual void OnGetUserEmailResponse(const std::string& user_email) = 0;
+    // Invoked when there is a network error or upon receiving an
+    // invalid response.
+    virtual void OnNetworkError(int response_code) = 0;
+  };
+
+  GaiaUserEmailFetcher(net::URLRequestContextGetter* context_getter);
+  ~GaiaUserEmailFetcher();
+
+  void GetUserEmail(const std::string& oauth_access_token,
+                    Delegate* delegate);
+
+ private:
+  // The guts of the implementation live in this class.
+  class Core;
+  scoped_refptr<Core> core_;
+  DISALLOW_COPY_AND_ASSIGN(GaiaUserEmailFetcher);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_GAIA_USER_EMAIL_FETCHER_H_