Fix MD display settings when the display supports a single resolution

chrome/browser/resources/settings/controls/settings_slider.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview
  * settings-slider wraps a paper-slider. It maps the slider's values from a
  * linear UI range to a range of real values.  When |value| does not map exactly
  * to a tick mark, it interpolates to the nearest tick.
  *
@@ skipping 32 matching lines @@
   observers: [
     'valueChanged_(pref.*, tickValues.*)',
   ],
 
   /**
    * Sets the |pref.value| property to the value corresponding to the knob
    * position after a user action.
    * @private
    */
   onSliderChanged_: function() {
+    var sliderValue = isNaN(this.$.slider.immediateValue)
+                         ? this.$.slider.value
+                         : this.$.slider.immediateValue;
+
     var newValue;
     if (this.tickValues && this.tickValues.length > 0)
-      newValue = this.tickValues[this.$.slider.immediateValue];
+      newValue = this.tickValues[sliderValue];
     else
-      newValue = this.$.slider.immediateValue;
+      newValue = sliderValue;
 
     this.set('pref.value', newValue);
   },
 
   /** @private */
   computeDisableSlider_: function() {
     return this.disabled || this.isPrefEnforced();
   },
 
   /**
@@ skipping 58 matching lines @@
       if (difference < minDifference) {
         closestIndex = i;
         minDifference = difference;
       }
     }
 
     assert(typeof closestIndex != 'undefined');
     return closestIndex;
   },
 });