Settings WebUI cleanup: Declaratively listen for 'close' event when possible.

Bug: None
Change-Id: I3ab1fd657115a98baa6d88a11ecaf6d0457c83c7
Reviewed-on: https://chromium-review.googlesource.com/1101711
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567700}

chrome/browser/resources/settings/languages_page/languages_page.html

@@ -394,7 +394,8 @@
     </settings-animated-pages>
     <template is="dom-if" if="[[showAddLanguagesDialog_]]" restamp>
       <settings-add-languages-dialog languages="{{languages}}"
-          language-helper="[[languageHelper]]">
+          language-helper="[[languageHelper]]"
+          on-close="onAddLanguagesDialogClose_">
       </settings-add-languages-dialog>
     </template>
   </template>

chrome/browser/resources/settings/languages_page/languages_page.js

@@ -146,13 +146,12 @@ Polymer({
   onAddLanguagesTap_: function(e) {
     e.preventDefault();
     this.showAddLanguagesDialog_ = true;
-    this.async(function() {
-      const dialog = this.$$('settings-add-languages-dialog');
-      dialog.addEventListener('close', () => {
-        this.showAddLanguagesDialog_ = false;
-        cr.ui.focusWithoutInk(assert(this.$.addLanguages));
-      });
-    });
+  },
+
+  /** @private */
+  onAddLanguagesDialogClose_: function() {
+    this.showAddLanguagesDialog_ = false;
+    cr.ui.focusWithoutInk(assert(this.$.addLanguages));
   },
 
   /**

chrome/browser/resources/settings/printing_page/cups_printers.html

@@ -55,7 +55,8 @@
 
     <template is="dom-if" if="[[showCupsEditPrinterDialog_]]" restamp>
       <settings-cups-edit-printer-dialog id="editPrinterDialog"
-          active-printer="{{activePrinter}}">
+          active-printer="{{activePrinter}}"
+          on-close="onEditPrinterDialogClose_">
       </settings-cups-edit-printer-dialog>
     </template>
 

chrome/browser/resources/settings/printing_page/cups_printers.js

@@ -185,12 +185,11 @@ Polymer({
   /** @private */
   onShowCupsEditPrinterDialog_: function() {
     this.showCupsEditPrinterDialog_ = true;
-    this.async(function() {
-      const dialog = this.$$('settings-cups-edit-printer-dialog');
-      dialog.addEventListener('close', function() {
-        this.showCupsEditPrinterDialog_ = false;
-      }.bind(this));
-    });
+  },
+
+  /** @private */
+  onEditPrinterDialogClose_: function() {
+    this.showCupsEditPrinterDialog_ = false;
   },
 
   /**