Add unit test to check for broker FD leak

sandbox/linux/services/broker_process.h

 // 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 SANDBOX_LINUX_SERVICES_BROKER_PROCESS_H_
 #define SANDBOX_LINUX_SERVICES_BROKER_PROCESS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 79 matching lines @@
   bool is_child_;                  // Whether we're the child (broker process).
   bool fast_check_in_client_;      // Whether to forward a request that we know
                                    // will be denied to the broker.
   bool quiet_failures_for_tests_;  // Disable certain error message when
                                    // testing for failures.
   pid_t broker_pid_;               // The PID of the broker (child).
   const std::vector<std::string> allowed_r_files_;  // Files allowed for read.
   const std::vector<std::string> allowed_w_files_;  // Files allowed for write.
   int ipc_socketpair_;  // Our communication channel to parent or child.
   DISALLOW_IMPLICIT_CONSTRUCTORS(BrokerProcess);
+
+  friend class BrokerProcessTestHelper;
 };
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_LINUX_SERVICES_BROKER_PROCESS_H_