Adding pref to store the user-selected proximity threshold.

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 1088 matching lines @@
     </message>
     <message name="IDS_SETTINGS_EASY_UNLOCK_TURN_OFF_ERROR_TITLE" desc="The title text on the Easy unlock turn off dialog when Easy unlock could not be turned off because there is a server error.">
       Smart Lock is unavailable
     </message>
     <message name="IDS_SETTINGS_EASY_UNLOCK_TURN_OFF_ERROR_MESSAGE" desc="The text on the Easy unlock turn off dialog when Easy unlock could not be turned off because there is a server error.">
       Smart Lock is currently unavailable. Please try again later.
     </message>
     <message name="IDS_SETTINGS_EASY_UNLOCK_TURN_OFF_RETRY" desc="The label text of the retry button on the Easy unlock turn off dialog when Easy unlock could not be turned off because there is a server error.">
       Retry
     </message>
+    <message name="IDS_SETTINGS_EASY_UNLOCK_PROXIMITY_THRESHOLD_LABEL" desc="The text on the Easy unlock settings page indicating how close the phone should be for unlock to work.">
+      Only unlock this Chromebook when your phone is
+    </message>
+    <message name="IDS_SETTINGS_EASY_UNLOCK_PROXIMITY_THRESHOLD_VERY_CLOSE" desc="The text on the Easy unlock settings page indicating the phone should be very close for the unlock to work.">
+      very close
+    </message>
+    <message name="IDS_SETTINGS_EASY_UNLOCK_PROXIMITY_THRESHOLD_CLOSE" desc="The text on the Easy unlock settings page indicating the phone should be close for the unlock to work.">
+      close
+    </message>
+    <message name="IDS_SETTINGS_EASY_UNLOCK_PROXIMITY_THRESHOLD_FAR" desc="The text on the Easy unlock settings page indicating the phone can far for the unlock to work.">

[Tim Song, 2017/07/07 21:48:24]

nit: can be far

[sacomoto, 2017/07/10 16:54:07]

Done.

+      far
+    </message>
+    <message name="IDS_SETTINGS_EASY_UNLOCK_PROXIMITY_THRESHOLD_VERY_FAR" desc="The text on the Easy unlock settings page indicating the phone can be very far for the unlock to work.">
+      very far
+    </message>
 
     <!-- Strings specific to the Settings Internet Page -->
     <message name="IDS_SETTINGS_INTERNET" desc="Name of the settings page which displays internet preferences.">
       Network
     </message>
     <message name="IDS_SETTINGS_INTERNET_CONFIG" desc="Name of the settings page for configuring a network.">
       Configure network
     </message>
     <message name="IDS_SETTINGS_INTERNET_DETAIL" desc="Name of the settings page which displays network details.">
       Network Details
@@ skipping 2074 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>