MD Settings: Restore focus when channel switcher dialog is closed.

chrome/browser/resources/settings/about_page/detailed_build_info.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="about_page_browser_proxy.html">
 <link rel="import" href="channel_switcher_dialog.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="chrome://resources/cr_elements/policy/cr_policy_indicator.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 
 <dom-module id="settings-detailed-build-info">
@@ skipping 35 matching lines @@
         </paper-button>
         <template is="dom-if" if="[[!canChangeChannel_]]">
           <cr-policy-indicator
               name="[[getChangeChannelIndicatorSourceName_(canChangeChannel_)]]"
               indicator-type="[[getChangeChannelIndicatorType_(
                   canChangeChannel_)]]">
           </cr-policy-indicator>
         </template>
       </div>
       <template is="dom-if" if="[[showChannelSwitcherDialog_]]" restamp>
-        <settings-channel-switcher-dialog></settings-channel-switcher-dialog>
+        <settings-channel-switcher-dialog
+            on-close="onChannelSwitcherDialogClosed_">
+        </settings-channel-switcher-dialog>
       </template>
     </div>
     <div class="settings-box two-line single-column"
         hidden$="[[!shouldShowVersion_(versionInfo_.arcVersion)]]">
       <div>$i18n{aboutArcVersionLabel}</div>
       <div class="secondary" id="arcVersion">[[versionInfo_.arcVersion]]</div>
     </div>
     <div class="settings-box two-line single-column">
       <div>Blink</div><!-- No need to localize. -->
       <div class="secondary">$i18n{aboutBlinkVersion}</div>
@@ skipping 10 matching lines @@
       <div>$i18n{aboutCommandLineLabel}</div>
       <div id="command-line" class="secondary">$i18n{aboutCommandLine}</div>
     </div>
     <div class="settings-box two-line single-column">
       <div>$i18n{aboutBuildDateLabel}</div>
       <div class="secondary">$i18n{aboutBuildDate}</div>
     </div>
   </template>
   <script src="detailed_build_info.js"></script>
 </dom-module>