Add "panel_fitting" GPU feature type and use it for mirror mode.

ash/ash_switches.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 ASH_ASH_SWITCHES_H_
 #define ASH_ASH_SWITCHES_H_
 
 #include "ash/ash_export.h"
 
 namespace ash {
 namespace switches {
 
 // Note: If you add a switch, consider if it needs to be copied to a subsequent
 // command line if the process executes a new copy of itself.  (For example,
 // see chromeos::LoginUtil::GetOffTheRecordCommandLine().)
 
 // Please keep alphabetized.
 ASH_EXPORT extern const char kAshConstrainPointerToRoot[];
 ASH_EXPORT extern const char kAshDebugShortcuts[];
+ASH_EXPORT extern const char kAshDisablePanelFitting[];
 ASH_EXPORT extern const char kAshDisableWorkspace2[];
 ASH_EXPORT extern const char kAshEnableAdvancedGestures[];
 ASH_EXPORT extern const char kAshEnableOak[];
 ASH_EXPORT extern const char kAshNotifyDisabled[];
 ASH_EXPORT extern const char kAshSecondaryDisplayLayout[];
 ASH_EXPORT extern const char kAshTouchHud[];
 ASH_EXPORT extern const char kAshWindowAnimationsDisabled[];
 ASH_EXPORT extern const char kAuraGoogleDialogFrames[];
 ASH_EXPORT extern const char kAuraLegacyPowerButton[];
 ASH_EXPORT extern const char kAuraNoShadows[];
 
 }  // namespace switches
 }  // namespace ash
 
 #endif  // ASH_ASH_SWITCHES_H_