Examine source code of Google Voice Bulk Texter

{
  "manifest_version": 2,
  "name": "Google Voice Bulk Texter",
  "short_name": "Bulk Texter",
  "description": "Send personalized bulk SMS messages via Google Voice.",
  "version": "1.3.2",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Bulk SMS",
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://hangouts.google.com/webchat/*"
      ],
      "js": [
        "contentScripts/hangoutsListViewManager.js",
        "contentScripts/hangoutsThreadViewManager.js"
      ],
      "all_frames": true
    },
    {
      "matches": [
        "https://voice.google.com/*"
      ],
      "js": [
        "contentScripts/googleVoiceManager.js"
      ],
      "all_frames": true
    },
    {
      "matches": [
        "https://hangouts.google.com/webchat/*",
        "https://voice.google.com/*"
      ],
      "js": [
        "contentScripts/tools.js",
        "contentScripts/main.js"
      ],
      "all_frames": true
    }
  ],
  "icons": {
    "48": "icon48.png",
    "128": "icon.png"
  },
  "permissions": [
    "clipboardWrite",
    "clipboardRead",
    "storage"
  ]
}