[MD settings] show icon when slider controlled by something

chrome/browser/resources/settings/device_page/display.html

 <link rel="import" href="chrome://resources/cr_elements/cr_slider/cr_slider.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/md_select_css.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-tabs/paper-tabs.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-toggle-button/paper-toggle-button.html">
 <link rel="import" href="display_layout.html">
@@ skipping 96 matching lines @@
         </div>
       </div>
       <div class="settings-box embedded two-line">
         <div class="start textarea layout vertical">
           <div>$i18n{displayResolutionTitle}</div>
           <div class="secondary layout self-start">
             [[getResolutionText_(selectedDisplay, selectedModeIndex_)]]
           </div>
         </div>
         <cr-slider disabled="[[!enableSetResolution_(selectedDisplay)]]"
-            tick-values="[[modeValues_]]" value="{{selectedModeIndex_}}"
+            tick-values="[[modeValues_]]" pref="{{pref}}"
             on-change="onSelectedModeChange_">
         </cr-slider>
       </div>
       <div class="settings-box embedded">
         <div class="start textarea">$i18n{displayOrientation}</div>
         <div class="md-select-wrapper">
           <select class="md-select" value="[[selectedDisplay.rotation]]"
               on-change="onOrientationChange_">
             <option value="0">$i18n{displayOrientationStandard}</option>
             <option value="90">90</option>
@@ skipping 32 matching lines @@
           </div>
         </div>
         <button class="subpage-arrow" is="paper-icon-button-light"
             aria-label="$i18n{displayTouchCalibrationTitle}"
             aria-describedby="touchCalibrationSecondary"></button>
       </div>
     </div>
   </template>
   <script src="display.js"></script>
 </dom-module>