[MD settings] show icon when slider controlled by something

ui/webui/resources/cr_elements/cr_slider/cr_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
  * cr-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.
  *
  * Unlike paper-slider, there is no distinction between value and
  * immediateValue; when either changes, the |value| property is updated.
  */
 Polymer({
   is: 'cr-slider',
 
+  behaviors: [CrPolicyPrefBehavior],
+
   properties: {
-    /** The value the slider represents and controls. */
-    value: {
-      type: Number,
-      notify: true,
-    },
+    pref: Object,
 
     /** @type {!Array<number>} Values corresponding to each tick. */
     tickValues: {type: Array, value: []},
 
-    disabled: {
-      type: Boolean,
-      value: false,
-      reflectToAttribute: true,
-    },
-
     min: Number,
 
     max: Number,
 
     labelMin: String,
 
     labelMax: String,
   },
 
   observers: [
-    'valueChanged_(value, tickValues.*)',
+    'valueChanged_(pref.*, tickValues.*)',
   ],
 
   /**
-   * Sets the |value| property to the value corresponding to the knob position
-   * after a user action.
+   * Sets the |pref.value| property to the value corresponding to the knob
+   * position after a user action.
    * @private
    */
   onSliderChanged_: function() {
+    var newValue;
     if (this.tickValues && this.tickValues.length > 0)
-      this.value = this.tickValues[this.$.slider.immediateValue];
+      newValue = this.tickValues[this.$.slider.immediateValue];
     else
-      this.value = this.$.slider.immediateValue;
+      newValue = this.$.slider.immediateValue;
+
+    this.set('pref.value', newValue);
+  },
+
+  /** @private */
+  shouldDisableSlider_: function() {
+    return this.disabled || this.isPrefEnforced();

[stevenjb, 2017/03/07 23:11:48]

Did you test this? I thought we needed to to use getAttribute for attributes?

[dschuyler, 2017/03/08 21:50:11]

or hasAttribute for boolean attributes.

   },
 
   /**
-   * Updates the knob position when |value| changes. If the knob is still being
-   * dragged, this instead forces |value| back to the current position.
+   * Updates the knob position when |pref.value| changes. If the knob is still
+   * being dragged, this instead forces |pref.value| back to the current
+   * position.
    * @private
    */
   valueChanged_: function() {
     // If |tickValues| is empty, simply set current value to the slider.
     if (this.tickValues.length == 0) {
-      this.$.slider.value = this.value;
+      this.$.slider.value = this.pref.value;
       return;
     }
 
     // First update the slider settings if |tickValues| was set.
     var numTicks = Math.max(1, this.tickValues.length);
     this.$.slider.max = numTicks - 1;
     // Limit the number of ticks to 10 to keep the slider from looking too busy.
     /** @const */ var MAX_TICKS = 10;
     this.$.slider.snaps = numTicks < MAX_TICKS;
     this.$.slider.maxMarkers = numTicks < MAX_TICKS ? numTicks : 0;
 
     if (this.$.slider.dragging && this.tickValues.length > 0 &&
-        this.value != this.tickValues[this.$.slider.immediateValue]) {
+        this.pref.value != this.tickValues[this.$.slider.immediateValue]) {
       // The value changed outside cr-slider but we're still holding the knob,
       // so set the value back to where the knob was.
       // Async so we don't confuse Polymer's data binding.
       this.async(function() {
-        this.value = this.tickValues[this.$.slider.immediateValue];
+        var newValue = this.tickValues[this.$.slider.immediateValue];
+        this.set('pref.value', newValue);
       });
       return;
     }
 
     // Convert from the public |value| to the slider index (where the knob
     // should be positioned on the slider).
-    var sliderIndex =
-        this.tickValues.length > 0 ? this.tickValues.indexOf(this.value) : 0;
+    var sliderIndex = this.tickValues.length > 0 ?
+        this.tickValues.indexOf(this.pref.value) :
+        0;
     if (sliderIndex == -1) {
       // No exact match.
-      sliderIndex = this.findNearestIndex_(this.tickValues, this.value);
+      sliderIndex = this.findNearestIndex_(this.tickValues, this.pref.value);
     }
     this.$.slider.value = sliderIndex;
   },
 
   /**
    * Returns the index of the item in |arr| closest to |value|.
    * @param {!Array<number>} arr
    * @param {number} value
    * @return {number}
    * @private
    */
   findNearestIndex_: function(arr, value) {
     var closestIndex;
     var minDifference = Number.MAX_VALUE;
     for (var i = 0; i < arr.length; i++) {
       var difference = Math.abs(arr[i] - value);
       if (difference < minDifference) {
         closestIndex = i;
         minDifference = difference;
       }
     }
 
     assert(typeof closestIndex != 'undefined');
     return closestIndex;
   },
 });