桌面捕獲鉻插件

我正在開發一個捕獲桌面屏幕的Chrome插件。我使用這裏給出的示例插件示例... https://developer.chrome.com/extensions/samples#desktop-capture-example 但在本例中，當我們單擊開始按鈕時會彈出一個對話框，詢問用戶要分享哪個屏幕或窗口，但我想共享當前屏幕做了哪些更改我在做這個代碼桌面捕獲鉻插件

// Copyright 2013 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. 

function gotStream(stream) { 
    console.log("Received local stream"); 
    var video = document.querySelector("video"); 
    video.src = URL.createObjectURL(stream); 
    localstream = stream; 
    stream.onended = function() { console.log("Ended"); }; 
} 

function getUserMediaError() { 
    console.log("getUserMedia() failed."); 
} 

function onAccessApproved(id) { 
if (!id) { 
    console.log("Access rejected."); 
    return; 
} 
navigator.webkitGetUserMedia({ 
audio:false, 
video: { mandatory: { chromeMediaSource: "desktop", 
         chromeMediaSourceId: id } } 
    }, gotStream, getUserMediaError); 
} 

var pending_request_id = null; 

document.querySelector('#start').addEventListener('click', function(e) { 
pending_request_id = chrome.desktopCapture.chooseDesktopMedia(
["screen"], onAccessApproved); 
}); 

document.querySelector('#cancel').addEventListener('click', function(e) { 
if (pending_request_id != null) { 
chrome.desktopCapture.cancelChooseDesktopMedia(pending_request_id); 
} 
});

應該是什麼chromeMediaSourceId的值，以使默認選擇是當前屏幕;

基本上我想避免這種屏幕.. enter image description here