Examine source code of Web Canvas

{
  "name": "Web Canvas",
  "manifest_version": 2,
  "version": "3.1",
  "description": "A powerful vector based annotation tool to draw or write anything on web.",
  "content_scripts": [
    {
      "js": [
        "content.js"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {},
  "permissions": [
    "tabs"
  ],
  "web_accessible_resources": [
    "*.html"
  ],
  "icons": {
    "16": "pencil16.png",
    "32": "pencil32.png",
    "64": "pencil64.png",
    "128": "pencil128.png"
  }
}