Examine source code of Layout Debugger

{
  "manifest_version" : 2 ,
  "name" : "Layout Debugger",
  "short_name" : "Layout Debugger",
  "description" : "Chrome extension for highlighting DOM elements to better debug layout issues",
  "version" : "1.7",
  "author": "Chris Snowden",
  "icons" : {
    "19" : "images/icon19dark.png",
    "38" : "images/icon38dark.png",
    "128" : "images/icon128dark.png"
  },
  "browser_action" : {
    "default_icon" : {
      "19" : "images/icon19dark.png",
      "38" : "images/icon38dark.png"
    },
    "default_title" : "Toggle highlighter"
  },
  "background" : {
    "scripts" : [
      "background.js" 
    ],
    "persistent" : false 
  },
  "content_scripts" : [
    {
      "matches" : [
        "<all_urls>" 
      ],
      "js" : [
        "highlight.js" 
      ]
    }
  ],
  "permissions" : [
    "activeTab" 
  ],
  "web_accessible_resources" : [
    "images/icon19dark.png",
    "images/icon38dark.png",
    "images/icon128dark.png",
    "highlight.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{624f9a0a-b329-447c-9bd5-cd51d1cdd0e0}"
    }
  }
}