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

content/public/common/content_switches.cc

 // 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.
 
 #include "content/public/common/content_switches.h"
 
 namespace switches {
 
 // By default, file:// URIs cannot read other file:// URIs. This is an
 // override for developers who need the old behavior for testing.
@@ skipping 696 matching lines @@
 
 // Sets the width and height above which a composited layer will get tiled.
 const char kMaxUntiledLayerWidth[]          = "max-untiled-layer-width";
 const char kMaxUntiledLayerHeight[]         = "max-untiled-layer-height";
 
 const char kEnableFixedPositionCreatesStackingContext[]
     = "enable-fixed-position-creates-stacking-context";
 const char kDisableFixedPositionCreatesStackingContext[]
     = "disable-fixed-position-creates-stacking-context";
 
+const char kDisablePanelFitting[]            = "disable-panel-fitting";
+
 }  // namespace switches