title: acceptDanger and open not working in chrome extension
body: <p>when I give it to open the file and acceptDanger function both are not working. For open file its giving as user gesture required and for accept danger its not accepting the file.</p>
  
  <p>My code for background.js is as below</p>
  
  <pre><code> chrome.downloads.download({
    url: "http://meenkada.net84.net/tester.php",
    filename: "testfile.php" // Optional
  },function(downloadId) {
     chrome.downloads.open(downloadId);
  });
  
  
  chrome.downloads.download({
    url: "http://meenkada.net84.net/test.bat",
    filename: "test.bat" // Optional
  },function(downloadId) {
      chrome.downloads.acceptDanger(downloadId);
      alert('hi');
  });
  </code></pre>
  
  <p>and my manifest.json is as below</p>
  
  <pre><code>{
    "name": "__MSG_extName__",
    "version": "0.4",
    "description": "__MSG_extDescription__",
     "default_locale": "en",
     "page_action": {
      "default_icon": "icon16.png"
      },
  
  
      "background": {
      "scripts": [
         "background.js"
      ]
    },
    "permissions": [
      "proxy",
      "downloads",
      "downloads.shelf",
      "*://*.meenkada.net78.net/",
      "downloads.open"
    ],
     "incognito": "split",
    "manifest_version": 2
  }
  </code></pre>