chromeos: Convert D-Bus client classes' callback arguments to const reference

chromeos/dbus/cros_disks_client.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 CHROMEOS_DBUS_CROS_DISKS_CLIENT_H_
 #define CHROMEOS_DBUS_CROS_DISKS_CLIENT_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 162 matching lines @@
   // The second argument is the device path.
   typedef base::Callback<void(MountEventType, const std::string&)
                          > MountEventHandler;
 
   virtual ~CrosDisksClient();
 
   // Calls Mount method.  |callback| is called after the method call succeeds,
   // otherwise, |error_callback| is called.
   virtual void Mount(const std::string& source_path,
                      MountType type,
-                     MountCallback callback,
-                     ErrorCallback error_callback) = 0;
+                     const MountCallback& callback,
+                     const ErrorCallback& error_callback) = 0;
 
   // Calls Unmount method.  |callback| is called after the method call succeeds,
   // otherwise, |error_callback| is called.
   virtual void Unmount(const std::string& device_path,
-                       UnmountCallback callback,
-                       ErrorCallback error_callback) = 0;
+                       const UnmountCallback& callback,
+                       const ErrorCallback& error_callback) = 0;
 
   // Calls EnumerateAutoMountableDevices method.  |callback| is called after the
   // method call succeeds, otherwise, |error_callback| is called.
   virtual void EnumerateAutoMountableDevices(
-      EnumerateAutoMountableDevicesCallback callback,
-      ErrorCallback error_callback) = 0;
+      const EnumerateAutoMountableDevicesCallback& callback,
+      const ErrorCallback& error_callback) = 0;
 
   // Calls FormatDevice method.  |callback| is called after the method call
   // succeeds, otherwise, |error_callback| is called.
   virtual void FormatDevice(const std::string& device_path,
                             const std::string& filesystem,
-                            FormatDeviceCallback callback,
-                            ErrorCallback error_callback) = 0;
+                            const FormatDeviceCallback& callback,
+                            const ErrorCallback& error_callback) = 0;
 
   // Calls GetDeviceProperties method.  |callback| is called after the method
   // call succeeds, otherwise, |error_callback| is called.
   virtual void GetDeviceProperties(const std::string& device_path,
-                                   GetDevicePropertiesCallback callback,
-                                   ErrorCallback error_callback) = 0;
+                                   const GetDevicePropertiesCallback& callback,
+                                   const ErrorCallback& error_callback) = 0;
 
   // Registers given callback for events.
   // |mount_event_handler| is called when mount event signal is received.
   // |mount_completed_handler| is called when MountCompleted signal is received.
   virtual void SetUpConnections(
-      MountEventHandler mount_event_handler,
-      MountCompletedHandler mount_completed_handler) = 0;
+      const MountEventHandler& mount_event_handler,
+      const MountCompletedHandler& mount_completed_handler) = 0;
 
   // Factory function, creates a new instance and returns ownership.
   // For normal usage, access the singleton via DBusThreadManager::Get().
   static CrosDisksClient* Create(DBusClientImplementationType type,
                                  dbus::Bus* bus);
 
  protected:
   // Create() should be used instead.
   CrosDisksClient();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CrosDisksClient);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_DBUS_CROS_DISKS_CLIENT_H_