MD Settings: add 'preserve-focus' flag to fix iron-list focus bugs.

chrome/browser/resources/settings/bluetooth_page/bluetooth_subpage.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 
 <link rel="import" href="chrome://resources/cr_elements/cr_scrollable_behavior.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-spinner/paper-spinner.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-toggle-button/paper-toggle-button.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../icons.html">
 <link rel="import" href="../settings_shared_css.html">
@@ skipping 44 matching lines @@
     <div class="settings-box first header" hidden="[[!bluetoothToggleState]]">
       <div class="start">$i18n{bluetoothDeviceListPaired}</div>
     </div>
     <div id="noPairedDevices" class="list-frame"
         hidden="[[!showNoDevices_(bluetoothToggleState, pairedDeviceList_)]]">
       $i18n{bluetoothNoDevices}
     </div>
     <div id="pairedContainer" class="container"
         scrollable on-device-event="onDeviceEvent_"
         hidden="[[!showDevices_(bluetoothToggleState, pairedDeviceList_)]]">
-      <iron-list id="pairedDevices" class="vertical-list"
+      <iron-list id="pairedDevices" class="vertical-list" preserve-focus
           items="[[pairedDeviceList_]]"
           selection-enabled selected-item="{{selectedPairedItem_}}"
           scroll-target="pairedContainer">
         <template>
           <bluetooth-device-list-item actionable device="[[item]]"
               tabindex$="[[tabIndex]]">
           </bluetooth-device-list-item>
         </template>
       </iron-list>
     </div>
 
     <!-- Unpaired device list -->
     <div class="settings-box first header" hidden="[[!bluetoothToggleState]]">
       <div class="start">$i18n{bluetoothDeviceListUnpaired}</div>
       <paper-spinner active="[[showSpinner_]]">
       </paper-spinner>
     </div>
     <div id="noUnpairedDevices" class="list-frame"
         hidden="[[!showNoDevices_(bluetoothToggleState, unpairedDeviceList_)]]">
       $i18n{bluetoothNoDevicesFound}
     </div>
     <div id="unpairedContainer" class="container"
         scrollable on-device-event="onDeviceEvent_"
         hidden="[[!showDevices_(bluetoothToggleState, unpairedDeviceList_)]]">
-      <iron-list id="unpairedDevices" class="vertical-list"
+      <iron-list id="unpairedDevices" class="vertical-list" preserve-focus
           items="[[unpairedDeviceList_]]"
           selection-enabled selected-item="{{selectedUnpairedItem_}}"
           scroll-target="unpairedContainer">
         <template>
           <bluetooth-device-list-item actionable device="[[item]]"
               tabindex$="[[tabIndex]]">
           </bluetooth-device-list-item>
         </template>
       </iron-list>
     </div>
 
     <bluetooth-device-dialog id="deviceDialog"
         bluetooth-private="[[bluetoothPrivate]]"
         dialog-id="[[dialogId_]]"
         error-message="[[errorMessage_]]"
         on-close="onDialogClose_"
         on-device-event="onDeviceEvent_"
         pairing-device="[[pairingDevice_]]">
     </bluetooth-device-dialog>
 
   </template>
   <script src="bluetooth_subpage.js"></script>
 </dom-module>