Create a Tether section in the system tray network list.

ash/ash_chromeos_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- ChromeOS-specific strings (included from ash_strings.grd).
      Everything in this file is wrapped in <if expr="chromeos">. -->
 <grit-part>
 
   <!-- Device types -->
   <message name="IDS_ASH_CHROMEBASE" desc="The device name for a Chromebase (versus say Chromebox)">
     Chromebase
   </message>
   <message name="IDS_ASH_CHROMEBIT" desc="The device name for a Chromebit (versus say Chromebox)">
@@ skipping 502 matching lines @@
   </message>
   <message name="IDS_ASH_STATUS_TRAY_WIFI_SCANNING_MESSAGE" desc="Scanning for wifi networks">
     Searching for Wi-Fi networks...
   </message>
   <message name="IDS_ASH_STATUS_TRAY_NETWORK_CELLULAR" desc="The label used in the tray popup to separate cellular networks.">
     Cellular
   </message>
   <message name="IDS_ASH_STATUS_TRAY_NETWORK_WIFI" desc="The label used in the tray popup to separate Wi-Fi networks.">
     Wi-Fi
   </message>
+  <message name="IDS_ASH_STATUS_TRAY_NETWORK_TETHER" desc="The label used in the tray popup to separate Instant Tethering networks.">
+    Instant Tethering
+  </message>
   <message name="IDS_ASH_STATUS_TRAY_ADD_CONNECTION" desc="Title for control to add a new network connection." >
     Add connection
   </message>
 
   <message name="IDS_ASH_VIRTUAL_KEYBOARD_TRAY_ACCESSIBLE_NAME" desc="The accessible text for virtual keyboard icon in status tray.">
     Show on-screen keyboard
   </message>
   <message name="IDS_ASH_DISPLAY_FAILURE_ON_MIRRORING" desc="An error message to show that the system failed to enter the mirroring mode.">
     Could not mirror displays since no supported resolutions found. Entered extended desktop instead.
   </message>
@@ skipping 99 matching lines @@
            desc="Notification message to tell users about the deprecation of Shift+ESC shortcut to show the task manager.">
     The shortcut to open the task manager has changed. Please use <ph name="NEW_SHORTCUT">$1<ex>Search+Esc</ex></ph> instead of <ph name="OLD_SHORTCUT">$2<ex>Shift+Esc</ex></ph>.
   </message>
 
   <!-- Notification that an accelerator was pressed, so the user knows how to toggle it back -->
   <message name="IDS_HIGH_CONTRAST_ACCEL_MSG"
            desc="Notification message to tell users that they just pressed the Search+Shift+H shortcut to toggle High Contrast Mode, and that pressing it again will toggle it off.">
     High Contrast Mode enabled. Press Search+Shift+H again to toggle it off.
   </message>
 </grit-part>