Count String Length

{
    "update_url": "https:\/\/clients2.google.com\/service\/update2\/crx",
    "name": "Count String Length",
    "version": "0.1",
    "manifest_version": 2,
    "description": "calculate selected text's length (strlen)",
    "icons": {
        "16": "icon_16.png",
        "128": "icon_128.png"
    },
    "background": {
        "persistent": false,
        "scripts": [
            "bg.js"
        ]
    },
    "permissions": [
        "",
        "contextMenus"
    ],
    "browser_action": {
        "default_title": "\u4e2d\u6587\u7b80\u7e41\u5b57\u4f53\u8f6c\u6362",
        "default_icon": "icon_128.png",
        "default_popup": "popup.html"
    }
}