Examine source code of Clear

{
  "manifest_version": 2,
  "name": "Clear",
  "description": "Unsubscribe from emails with one click.",
  "version": "1.0.0",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "16": "images/m16.png",
    "48": "images/m48.png",
    "128": "images/m128.png"
  },
  "page_action": {
    "default_icon": {
      "19": "images/m19.png",
      "38": "images/m38.png"
    },
    "default_title": "Unsubscribe from emails like this"
  },
  "permissions": [
    "storage",
    "tabs",
    "http://mail.google.com/*",
    "https://mail.google.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://*/*",
        "http://*/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ]
}