MD Settings: fix focus-row-behavior allowing invisible focus on rows.

chrome/browser/resources/settings/focus_row_behavior.js

 // Copyright 2017 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.
 
 /**
  * @param {{lastFocused: Object}} listItem
  * @constructor
  * @implements {cr.ui.FocusRow.Delegate}
  */
 function FocusRowDelegate(listItem) {
   /** @private */
   this.listItem_ = listItem;
 }
 
 FocusRowDelegate.prototype = {
   /**
+   * This function gets called when the [focus-row-control] element receives
+   * the focus event.
    * @override
    * @param {!cr.ui.FocusRow} row
    * @param {!Event} e
    */
   onFocus: function(row, e) {
     this.listItem_.lastFocused = e.path[0];
+    this.listItem_.tabIndex = -1;
   },
 
   /**
    * @override
    * @param {!cr.ui.FocusRow} row The row that detected a keydown.
    * @param {!Event} e
    * @return {boolean} Whether the event was handled.
    */
   onKeydown: function(row, e) {
     // Prevent iron-list from changing the focus on enter.
@@ skipping 97 matching lines @@
       var controls = this.root.querySelectorAll('[focus-row-control]');
 
       for (var i = 0; i < controls.length; i++) {
         this.row_.addItem(
             controls[i].getAttribute('focus-type'),
             /** @type {HTMLElement} */ (controls[i]));
       }
     }
   },
 
-  /** @private */
+  /**
+   * This function gets called when the row itself receives the focus event.
+   * @private
+   */
   onFocus_: function() {
     if (this.mouseFocused_) {
       this.mouseFocused_ = false;  // Consume and reset flag.
       return;
     }
 
     if (this.lastFocused) {
       this.row_.getEquivalentElement(this.lastFocused).focus();
     } else {
       var firstFocusable = assert(this.row_.getFirstFocusable());
@@ skipping 12 matching lines @@
   /** @private */
   onMouseDown_: function() {
     this.mouseFocused_ = true;  // Set flag to not do any control-focusing.
   },
 
   /** @private */
   onBlur_: function() {
     this.mouseFocused_ = false;  // Reset flag since it's not active anymore.
   }
 };