Adding pref to store the user-selected proximity threshold.

chrome/browser/resources/settings/people_page/lock_screen.js

Index: chrome/browser/resources/settings/people_page/lock_screen.js
diff --git a/chrome/browser/resources/settings/people_page/lock_screen.js b/chrome/browser/resources/settings/people_page/lock_screen.js
index f5b62a7980d04b2c8fd21871d1b603a0ba95829a..4c046e29b46d895d93c0823f13055af2b327c1df 100644
--- a/chrome/browser/resources/settings/people_page/lock_screen.js
+++ b/chrome/browser/resources/settings/people_page/lock_screen.js
@@ -14,6 +14,18 @@
  * </settings-lock-screen>
  */
 
+/**
+ * Possible values of the proximity threshould displayed to the user.
+ * This should be kept in sync with the enum defined here:
+ * components/proximity_auth/proximity_monitor_impl.cc
+ */
+settings.EasyUnlockProximityThreshold = {
+  VERY_CLOSE: 0,
+  CLOSE: 1,
+  FAR: 2,
+  VERY_FAR: 3,
+};
+
 Polymer({
   is: 'settings-lock-screen',
 
@@ -118,6 +130,36 @@ Polymer({
       readOnly: true,
     },
 
+    /**
+     * Returns the proximity threshold mapping to be displayed in the
+     * threshold selector dropdown menu.

[stevenjb, 2017/07/17 16:43:37]

* @type {DropdownMenuOptionList}

(You will need to include settings_dropdown_menu.js in compiled_resources2.gyp).

[sacomoto, 2017/07/20 19:50:15]

Done.

+     */
+    easyUnlockProximityThresholdMapping_: {
+      type: Array,
+      value: function() {
+        return [
+          {
+            value: settings.EasyUnlockProximityThreshold.VERY_CLOSE,
+            name:
+                loadTimeData.getString('easyUnlockProximityThresholdVeryClose')
+          },
+          {
+            value: settings.EasyUnlockProximityThreshold.CLOSE,
+            name: loadTimeData.getString('easyUnlockProximityThresholdClose')
+          },
+          {
+            value: settings.EasyUnlockProximityThreshold.FAR,
+            name: loadTimeData.getString('easyUnlockProximityThresholdFar')
+          },
+          {
+            value: settings.EasyUnlockProximityThreshold.VERY_FAR,
+            name: loadTimeData.getString('easyUnlockProximityThresholdVeryFar')
+          }
+        ];
+      },
+      readOnly: true,
+    },
+
     /** @private */
     showEasyUnlockTurnOffDialog_: {
       type: Boolean,