Add Core::ReplaceHandleWithReducedRights().

mojo/edk/system/dispatcher.h

 // Copyright 2013 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 MOJO_EDK_SYSTEM_DISPATCHER_H_
 #define MOJO_EDK_SYSTEM_DISPATCHER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 263 matching lines @@
   virtual MojoResult DuplicateDispatcherImplNoLock(
       util::RefPtr<Dispatcher>* new_dispatcher)
       MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   // This is called by |CreateEquivalentDispatcherAndCloseNoLock()|. It should
   // "close" this dispatcher and return a new one equivalent to it. Note:
   // Probably the first thing an implementation should do is call
   // |CancelAllStateNoLock()| (or equivalent); unlike |CloseNoLock()|,
   // |CreateEquivalentDispatcherAndCloseNoLock()| does not do this
   // automatically.
+  //
+  // If the new dispatcher will be enqueued on a message pipe, then
+  // |message_pipe|/|port| will be provided (since there may be some
+  // special-casing necessary due to locking considerations); otherwise,
+  // |message_pipe| will be null (and |port| will be meaningless).
   virtual util::RefPtr<Dispatcher> CreateEquivalentDispatcherAndCloseImplNoLock(
       MessagePipe* message_pipe,
       unsigned port) MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex_) = 0;
 
   // These are to be overridden by subclasses (if necessary). They are never
   // called after the dispatcher has been closed. See the descriptions of the
   // methods without the "ImplNoLock" for more information.
   virtual MojoResult WriteMessageImplNoLock(
       UserPointer<const void> bytes,
       uint32_t num_bytes,
@@ skipping 161 matching lines @@
 
 // So logging macros and |DCHECK_EQ()|, etc. work.
 inline std::ostream& operator<<(std::ostream& out, Dispatcher::Type type) {
   return out << static_cast<int>(type);
 }
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_DISPATCHER_H_