Convert some more |base::Lock|s to |mojo::system::Mutex|s.

mojo/edk/system/incoming_endpoint.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 MOJO_EDK_SYSTEM_INCOMING_ENDPOINT_H_
 #define MOJO_EDK_SYSTEM_INCOMING_ENDPOINT_H_
 
 #include <stddef.h>
 
 #include "base/memory/ref_counted.h"
-#include "base/synchronization/lock.h"
 #include "mojo/edk/system/channel_endpoint_client.h"
 #include "mojo/edk/system/message_in_transit_queue.h"
+#include "mojo/edk/system/mutex.h"
 #include "mojo/edk/system/system_impl_export.h"
 #include "mojo/public/cpp/system/macros.h"
 
 struct MojoCreateDataPipeOptions;
 
 namespace mojo {
 namespace system {
 
 class ChannelEndpoint;
 class DataPipe;
@@ skipping 21 matching lines @@
   // wasn't called (but |Init()| was).
   void Close();
 
   // |ChannelEndpointClient| methods:
   bool OnReadMessage(unsigned port, MessageInTransit* message) override;
   void OnDetachFromChannel(unsigned port) override;
 
  private:
   ~IncomingEndpoint() override;
 
-  base::Lock lock_;  // Protects the following members.
-  scoped_refptr<ChannelEndpoint> endpoint_;
-  MessageInTransitQueue message_queue_;
+  Mutex mutex_;
+  scoped_refptr<ChannelEndpoint> endpoint_ MOJO_GUARDED_BY(mutex_);
+  MessageInTransitQueue message_queue_ MOJO_GUARDED_BY(mutex_);
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(IncomingEndpoint);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_INCOMING_ENDPOINT_H_