Use md-select instead of paper-dropdown-menu-light in display.html

chrome/browser/resources/settings/device_page/display.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-display' is the settings subpage for display settings.
  */
 
 cr.define('settings.display', function() {
@@ skipping 136 matching lines @@
     }
     return 0;
   },
 
   /** @private */
   selectedDisplayChanged_: function() {
     // Set maxModeIndex first so that the slider updates correctly.
     if (this.selectedDisplay.modes.length == 0) {
       this.maxModeIndex_ = 0;
       this.selectedModeIndex_ = 0;
-      return;
+    } else {
+      this.maxModeIndex_ = this.selectedDisplay.modes.length - 1;
+      this.selectedModeIndex_ =
+          this.getSelectedModeIndex_(this.selectedDisplay);
     }
-    this.maxModeIndex_ = this.selectedDisplay.modes.length - 1;
-    this.selectedModeIndex_ = this.getSelectedModeIndex_(this.selectedDisplay);
+    this.$.orientation.value = this.selectedDisplay.rotation;

[dpapad, 2016/10/18 00:14:46]

Nit: Since your drodpown is not using dom-repeat, you can use 1-way data binding
without any worries here (all <option> instances are rendered in when ready() is
called). So no need to programmatically set the value.

<select .... value="[[this.selectedDisplay.rotation]]">

[stevenjb, 2016/10/18 00:43:11]

Yup. I just finished making this consistent with the internet changes.

   },
 
   /**
    * @param {!chrome.system.display.DisplayUnitInfo} selectedDisplay
    * @param {string} primaryDisplayId
    * @return {boolean}
    * @private
    */
   showMakePrimary_: function(selectedDisplay, primaryDisplayId) {
     return !!selectedDisplay && selectedDisplay.id != primaryDisplayId;
@@ skipping 101 matching lines @@
     assert(newIndex < this.selectedDisplay.modes.length);
     /** @type {!chrome.system.display.DisplayProperties} */ var properties = {
       displayMode: this.selectedDisplay.modes[newIndex]
     };
     settings.display.systemDisplayApi.setDisplayProperties(
         this.selectedDisplay.id, properties,
         this.setPropertiesCallback_.bind(this));
   },
 
   /**
-   * @param {!{detail: !{selected: string}}} e
+   * @param {!{target: !{value: string}}} e

[dpapad, 2016/10/18 00:14:46]

@param {!Event}

[stevenjb, 2016/10/18 00:43:11]

Acknowledged.

    * @private
    */
   onSetOrientation_: function(e) {
     /** @type {!chrome.system.display.DisplayProperties} */ var properties = {
-      rotation: parseInt(e.detail.selected, 10)
+      rotation: parseInt(e.target.value, 10)

[dpapad, 2016/10/18 00:14:46]

Cast to HTMLSelectElement to satisfy the compiler.

[stevenjb, 2016/10/18 00:43:10]

Acknowledged.

     };
     settings.display.systemDisplayApi.setDisplayProperties(
         this.selectedDisplay.id, properties,
         this.setPropertiesCallback_.bind(this));
   },
 
   /** @private */
   onMirroredTap_: function() {
     var id = '';
     /** @type {!chrome.system.display.DisplayProperties} */ var properties = {};
@@ skipping 42 matching lines @@
   },
 
   /** @private */
   setPropertiesCallback_: function() {
     if (chrome.runtime.lastError) {
       console.error(
           'setDisplayProperties Error: ' + chrome.runtime.lastError.message);
     }
   },
 });