Gmail Empty Subject Checker/Validator

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "manifest_version": 2,
  "name": "Gmail Empty Subject Checker/Validator",
  "short_name": "Gmail Subject Checker/Validator",
  "version": "1.1.0",
  "description": "In Gmail, this Chrome extension will not allow you to send an email if the Subject field is empty",
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/*"
      ],
      "js": [
        "extensionInjector.js"
      ],
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    "gmailJsLoader.js",
    "extension.js"
  ],
  "permissions": [
    "https://*/*"
  ],
  "icons": {
    "16": "fullscreen.png",
    "48": "fullscreen.png",
    "128": "fullscreen.png"
  }
}