Firefox overlay is seen opened even if Import Overlay is Cancelled.

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 111 matching lines @@
   /** @private */
   onActionButtonTap_: function() {
     if (this.isImportFromFileSelected_())
       this.browserProxy_.importFromBookmarksFile();
     else
       this.browserProxy_.importData(this.$.browserSelect.selectedIndex);
   },
 
   /** @private */
   closeDialog_: function() {
+    //During Closing the import dialog also send close to "import lock dialog "
+    //if it is shown on the screen.

[Ilya Sherman, 2017/03/29 06:29:02]

nit: Thanks for adding a comment here. I'd rephrase it something along the lines
of:

"It's possible for the user to close the import dialog while a sub-dialog is
still showing. Make sure to close that sub-dialog as well."

[nikhil.sahni, 2017/03/30 12:13:35]

Done.

+    this.browserProxy_.closeImportLockDialog();
     this.$.dialog.close();
   },
 
   /**
    * @return {boolean} Whether the import button should be disabled.
    * @private
    */
   shouldDisableImport_: function() {
     return this.hasImportStatus_(settings.ImportDataStatus.IN_PROGRESS) ||
         this.noImportDataTypeSelected_;
   },
 });