Introduce user customization of external HighDPI mode for 4K monitor.

tools/metrics/actions/actions.xml

 <!--
 Copyright 2014 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.
 -->
 
 <!--
 This file is a comprehensive list of Chrome user actions along with the owner
 and description for each user action.
 
@@ skipping 8343 matching lines @@
   <description>Settings: Device: Display settings: Orientation</description>
 </action>
 
 <action name="Options_DisplaySetPrimary">
   <owner>stevenjb@chromium.org</owner>
   <description>Settings: Device: Display settings: Make primary</description>
 </action>
 
 <action name="Options_DisplaySetResolution">
   <owner>stevenjb@chromium.org</owner>
-  <description>Settings: Device: Display settings: Resolution</description>
+  <description>
+    Settings: Device: Display settings: Display mode (i.e. resolution, UI-scale,
+    and device scale factor).
+  </description>
 </action>
 
 <action name="Options_DisplayToggleMirroring">
   <owner>stevenjb@chromium.org</owner>
   <description>Settings: Device: Display settings: Start mirroring</description>
 </action>
 
 <action name="Options_DnsPrefetchCheckbox_Disable">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>
@@ skipping 3020 matching lines @@
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>
 </action>
 
 <action name="webapps.AddShortcut.Bookmark">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>
 </action>
 
 </actions>