title: contextMenu not working in Chrome Packaged App
body: <p>I have a Chrome Packaged App and I can't seem to figure out how to add contextMenus to it. </p>
  
  <p>This is my manifest:</p>
  
  <pre><code>{
    "name": "Dialer",
    "version": "0.1",
    "manifest_version": 2,
    "permissions": [
      "contextMenus",
      "audioCapture"
    ],
    "app": {
      "background": {
        "scripts": ["background.js"]
      }
    },
    "icons": {
      "128":"icon_128.png"
    }
  }
  </code></pre>
  
  <p>and this is my background.js:</p>
  
  <pre><code>chrome.app.runtime.onLaunched.addListener(function() {
      chrome.contextMenus.create ({
          title: "%s", 
          contexts: ["all"],
          id: "right-click"
      });
  });
  </code></pre>
  
  <p>What am I doing wrong? The menu item doesn't appear when I right click.</p>
  
  <p>Thanks</p>