MD Settings: Defer opening Import Dialog dialog to prevent UI flicker

chrome/browser/resources/settings/people_page/import_data_dialog.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-import-data-dialog' is a component for importing
  * bookmarks and other data from other sources.
  */
 Polymer({
   is: 'settings-import-data-dialog',
@@ skipping 40 matching lines @@
   browserProxy_: null,
 
   /** @override */
   attached: function() {
     this.browserProxy_ = settings.ImportDataBrowserProxyImpl.getInstance();
     this.browserProxy_.initializeImportDialog().then(
         /** @param {!Array<!settings.BrowserProfile>} data */
         function(data) {
           this.browserProfiles_ = data;
           this.selected_ = this.browserProfiles_[0];
+
+          // Show the dialog only after the browser profiles data is populated
+          // to avoid UI flicker.
+          this.$.dialog.showModal();
         }.bind(this));
 
     this.addWebUIListener(
         'import-data-status-changed',
         /** @param {settings.ImportDataStatus} importStatus */
         function(importStatus) {
           this.importStatus_ = importStatus;
           if (this.hasImportStatus_(settings.ImportDataStatus.FAILED))
             this.closeDialog_();
         }.bind(this));
-
-    this.$.dialog.showModal();
   },
 
   /** @private */
   prefsChanged_() {
     this.noImportDataTypeSelected_ =
         !(this.getPref('import_history').value && this.selected_.history) &&
         !(this.getPref('import_bookmarks').value && this.selected_.favorites) &&
         !(this.getPref('import_saved_passwords').value &&
             this.selected_.passwords) &&
         !(this.getPref('import_search_engine').value &&
@@ skipping 47 matching lines @@
 
   /**
    * @return {boolean} Whether the import button should be disabled.
    * @private
    */
   shouldDisableImport_: function() {
     return this.hasImportStatus_(settings.ImportDataStatus.IN_PROGRESS) ||
         this.noImportDataTypeSelected_;
   },
 });