Adding method to create process using LowBox token in sandbox code.

sandbox/win/src/sid.h

 // Copyright (c) 2006-2008 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_SRC_SID_H_
 #define SANDBOX_SRC_SID_H_
 
+#include <string>
 #include <windows.h>
 
 namespace sandbox {
 
 // This class is used to hold and generate SIDS.
 class Sid {
  public:
   // Constructors initializing the object with the SID passed.
   // This is a converting constructor. It is not explicit.
   Sid(const SID *sid);
   Sid(WELL_KNOWN_SID_TYPE type);
 
   // Returns sid_.
   const SID *GetPSID() const;
 
+  // Returns sid based on wellknown or provided sid but with unique
+  // subauthority.
+  std::wstring GenerateUniqueSubAuthoritySid();
+
  private:
   BYTE sid_[SECURITY_MAX_SID_SIZE];
 };
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_SRC_SID_H_