DevTools: remove selections on dropdown menu open

third_party/WebKit/Source/devtools/front_end/ui/DropDownMenu.js

 // Copyright 2014 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.
 /**
  * @unrestricted
  */
 UI.DropDownMenu = class extends Common.Object {
   /**
    * @param {!Element} element
    */
   constructor(element) {
     super();
     /** @type {!Array.<!UI.DropDownMenu.Item>} */
     this._items = [];
 
     element.addEventListener('mousedown', this._onMouseDown.bind(this));
   }
 
   /**
    * @param {!Event} event
    */
   _onMouseDown(event) {
     if (event.which !== 1)
       return;
+
+    // Remove any selections to avoid native context menu items, for example 'Copy'.
+    var selection = UI.inspectorView.element.window().getSelection();

[lushnikov, 2017/03/03 04:11:00]

it would be nice if we can create context menus without this system subitems.

Let's try to improve our context menus!

+    selection.removeAllRanges();
+
     var menu = new UI.ContextMenu(event);
     for (var item of this._items)
       menu.appendCheckboxItem(item.title, this._itemHandler.bind(this, item.id), item.id === this._selectedItemId);
     menu.show();
   }
 
   /**
    * @param {string} id
    */
   _itemHandler(id) {
@@ skipping 21 matching lines @@
   }
 };
 
 /** @typedef {{id: string, title: string}} */
 UI.DropDownMenu.Item;
 
 /** @enum {symbol} */
 UI.DropDownMenu.Events = {
   ItemSelected: Symbol('ItemSelected')
 };