[Password Manager] Focus 'More options...' after closing export dialog

Focus should return to the item which caused the export modal dialog to
be opened, once the dialog is done.

Bug: 818619
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I0e67519aef1821e751e7dd90bab42b4321408442
Reviewed-on: https://chromium-review.googlesource.com/950774Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Christos Froussios <cfroussios@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542097}

chrome/browser/resources/settings/passwords_and_forms_page/passwords_section.js

@@ -554,6 +554,8 @@ Polymer({
   /** @private */
   onPasswordsExportDialogClosed_: function() {
     this.showPasswordsExportDialog_ = false;
+    cr.ui.focusWithoutInk(assert(this.activeDialogAnchor_));
+    this.activeDialogAnchor_ = null;
   },
 
   /**