Added unit tests for getCredentialsFromAuthCode.

remoting/host/setup/mock_oauth_client.cc

+// Copyright 2015 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.
+
+#include "remoting/host/setup/mock_oauth_client.h"
+
+namespace remoting {
+
+MockOAuthClient::~MockOAuthClient() {
+}
+
+void MockOAuthClient::GetCredentialsFromAuthCode(
+    const gaia::OAuthClientInfo& oauth_client_info,
+    const std::string& auth_code,
+    CompletionCallback on_done) {
+
+  on_done.Run(user_email_, refresh_token_);
+}
+
+}  // namespace remoting