Gmail 'Expand all' keyboard shortcut

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Gmail 'Expand all' keyboard shortcut",
  "description": "Press Alt+A to expand or collapse a Gmail thread",
  "version": "1.1",
  "manifest_version": 2,
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "commands": {
    "toggle-expand-all": {
      "suggested_key": {
        "default": "Alt+A"
      },
      "description": "Send a 'toggle-expand-all' event to the extension"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ],
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  }
}