MD Settings: Display: Add unified desktop control and modify api

chrome/app/settings_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Settings-specific strings (included from generated_resources.grd). -->
 <grit-part>
   <!-- Main Page -->
   <if expr="chromeos">
     <message name="IDS_SETTINGS_SECONDARY_USER_BANNER" desc="Banner displayed in settings page when the user is secondary in a multi-profile session.">
       Some settings belonging to <ph name="PRIMARY_EMAIL">$1<ex>john@google.com</ex></ph> are being shared with you. These settings only affect your account when using multiple sign-in.
     </message>
   </if>
 
@@ skipping 2818 matching lines @@
     </message>
     <message name="IDS_SETTINGS_DISPLAY_ARRANGEMENT_TITLE" desc="In Device Settings > Displays, the label for the display arrangement section.">
       Arrangement
     </message>
     <message name="IDS_SETTINGS_DISPLAY_ARRANGEMENT_TEXT" desc="In Device Settings > Displays, text describing to use a mouse to drag the displays and change the arrangement.">
       Drag to move a display
     </message>
     <message name="IDS_SETTINGS_DISPLAY_MIRROR" desc="In Device Settings > Displays, the label for the control for mirroring.">
       Mirroring
     </message>
+    <message name="IDS_SETTINGS_DISPLAY_UNIFIED_DESKTOP" desc="In Device Settings > Displays, the label for the control for the unified desktop feature.">
+      Allow windows to span displays
+    </message>
     <message name="IDS_SETTINGS_DISPLAY_SCREEN" desc="In Device Settings > Displays, the label for the dropdown menu for changing the dispay type.">
       Screen
     </message>
     <message name="IDS_SETTINGS_DISPLAY_SCREEN_PRIMARY" desc="The label for the dropdown menu list item to set the selected screen as primary display.">
       Primary display
     </message>
     <message name="IDS_SETTINGS_DISPLAY_SCREEN_EXTENDED" desc="The label for the dropdown menu list item to set the selected screen as extended display.">
       Extended display
     </message>
     <message name="IDS_SETTINGS_DISPLAY_RESOLUTION_TITLE" desc="In Device Settings > Displays, the label for the section for changing a display's resolution.">
@@ skipping 28 matching lines @@
     </message>
     <message name="IDS_SETTINGS_DISPLAY_OVERSCAN_RESIZE" desc="Label for resizing overscan calibration.">
       Shrink / Expand
     </message>
     <message name="IDS_SETTINGS_DISPLAY_OVERSCAN_POSITION" desc="Label for positioning overscan calibration.">
       Move
     </message>
     <message name="IDS_SETTINGS_DISPLAY_OVERSCAN_RESET" desc="Label for resetting overscan calibration.">
       Reset
     </message>
-    <message name="IDS_SETTINGS_DISPLAY_MIRRORING_ON" desc="Label indicating that the displays are currently mirrored">
-      On
-    </message>
-    <message name="IDS_SETTINGS_DISPLAY_MIRRORING_OFF" desc="Label indicating that the displays are currently not mirrored">
-      Off
-    </message>
     <message name="IDS_SETTINGS_DISPLAY_TOUCH_CALIBRATION_TITLE" desc="In Device Settings > Displays, the label for initiating touch calibration.">
       Calibrate touchscreen
     </message>
     <message name="IDS_SETTINGS_DISPLAY_TOUCH_CALIBRATION_TEXT" desc="In Device Settings > Displays, the sublabel for initiating touch calibration.">
       Set up and adjust the accuracy of your touchscreen
     </message>
 
     <!-- Storage -->
     <message name="IDS_SETTINGS_STORAGE_TITLE" desc="In Device Settings, the title for storage management.">
       Storage management
@@ skipping 80 matching lines @@
       System
     </message>
     <message name="IDS_SETTINGS_SYSTEM_HARDWARE_ACCELERATION_LABEL" desc="Label for the checkbox that forces Chrome to render via hardware acceleration (GPU) when available.">
       Use hardware acceleration when available
     </message>
     <message name="IDS_SETTINGS_SYSTEM_PROXY_SETTINGS_LABEL" desc="Label for the control that opens a user's network proxy settings.">
       Open proxy settings
     </message>
   </if>
 </grit-part>