Use list instead of pair to represent the set of displays.

ash/display/display_change_observer_chromeos.cc

 // 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.
 
 #include "ash/display/display_change_observer_chromeos.h"
 
 #include <algorithm>
 #include <map>
 #include <set>
 #include <string>
@@ skipping 138 matching lines @@
 DisplayChangeObserver::~DisplayChangeObserver() {
   ui::DeviceDataManager::GetInstance()->RemoveObserver(this);
   Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 ui::MultipleDisplayState DisplayChangeObserver::GetStateForDisplayIds(
     const ui::DisplayConfigurator::DisplayStateList& display_states) const {
   UpdateInternalDisplayId(display_states);
   if (display_states.size() != 2)
     return ui::MULTIPLE_DISPLAY_STATE_DUAL_EXTENDED;
-  DisplayIdPair pair = CreateDisplayIdPair(display_states[0]->display_id(),
+  DisplayIdList list = CreateDisplayIdList(display_states[0]->display_id(),
                                            display_states[1]->display_id());
-  DisplayLayout layout = Shell::GetInstance()->display_manager()->
-      layout_store()->GetRegisteredDisplayLayout(pair);
+  DisplayLayout layout = Shell::GetInstance()
+                             ->display_manager()
+                             ->layout_store()
+                             ->GetRegisteredDisplayLayout(list);
   return layout.mirrored ? ui::MULTIPLE_DISPLAY_STATE_DUAL_MIRROR :
                            ui::MULTIPLE_DISPLAY_STATE_DUAL_EXTENDED;
 }
 
 bool DisplayChangeObserver::GetResolutionForDisplayId(int64_t display_id,
                                                       gfx::Size* size) const {
   DisplayMode mode;
   if (!Shell::GetInstance()->display_manager()->GetSelectedModeForDisplayId(
            display_id, &mode))
     return false;
@@ skipping 126 matching lines @@
   }
   return 1.0f;
 }
 
 void DisplayChangeObserver::OnTouchscreenDeviceConfigurationChanged() {
   OnDisplayModeChanged(
       Shell::GetInstance()->display_configurator()->cached_displays());
 }
 
 }  // namespace ash