Get the default device scale factor from monitor

ui/base/ui_base_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 "ui/base/ui_base_switches.h"
 
 namespace switches {
 
+// The default device scale factor to apply to the browser UI and
+// the contents in the absence of a viewport meta tag.
+const char kDefaultDeviceScaleFactor[] = "default-device-scale-factor";
+
 // Enable support for touch events.
 const char kEnableTouchEvents[]             = "enable-touch-events";
 
 // The language file that we want to try to open. Of the form
 // language[-country] where language is the 2 letter code from ISO-639.
 const char kLang[]                          = "lang";
 
 // Load the locale resources from the given path. When running on Mac/Unix the
 // path should point to a locale.pak file.
 const char kLocalePak[]                     = "locale_pak";
 
 // Disable ui::MessageBox. This is useful when running as part of scripts that
 // do not have a user interface.
 const char kNoMessageBox[]                  = "no-message-box";
 
 // Enables UI changes that make it easier to use with a touchscreen.
 const char kTouchOptimizedUI[]              = "touch-optimized-ui";
 
 #if defined(OS_MACOSX)
 const char kDisableCompositedCoreAnimationPlugins[] =
     "disable-composited-core-animation-plugins";
 #endif
 
 }  // namespace switches