Do not double-unref send rights when using POLICY_SUBSTITUE_PORT.

sandbox/mac/policy.h

 // Copyright 2014 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_MAC_POLICY_H_
 #define SANDBOX_MAC_POLICY_H_
 
 #include <mach/mach.h>
 
 #include <map>
@@ skipping 24 matching lines @@
 // |substitute_port| must be NULL. If result is POLICY_SUBSTITUTE_PORT, then
 // |substitute_port| must not be NULL.
 struct SANDBOX_EXPORT Rule {
   Rule();
   explicit Rule(PolicyDecision result);
   explicit Rule(mach_port_t override_port);
 
   PolicyDecision result;
 
   // The Rule does not take ownership of this port, but additional send rights
-  // will be allocated to it before it is sent to a client.
+  // will be allocated to it before it is sent to a client. This name must
+  // denote a send right that can duplicated with MACH_MSG_TYPE_COPY_SEND.
   mach_port_t substitute_port;
 };
 
 // A SandboxPolicy maps bootstrap server names to policy Rules.
 typedef std::map<std::string, Rule> BootstrapSandboxPolicy;
 
 // Checks that a policy is well-formed.
 SANDBOX_EXPORT bool IsPolicyValid(const BootstrapSandboxPolicy& policy);
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_MAC_POLICY_H_