ElectronでChrome Extension使えるようにするまでのハマりどころ ref: http://qiita.com/inuscript/items/590c96041163d09467d5

file0.js

const {BrowserWindow} = electron;

const os = require('os')
const path = require('path')
const fs = require('fs')

function createWindow() {
  　:
  　:
  // react dev toolのID
  const id = "fmkadmapgofadopljbjfkapdkoienihi"

  // extensionの場所、"~/Library"だとダメだった
  const extensionDir = path.resolve(os.homedir(), "Library/Application Support/Google/Chrome/Default/Extensions/")

  // version指定
  const versions = fs.readdirSync(`${extensionDir}/${id}`).sort()
  const version = versions.pop()

  // 利用
  BrowserWindow.addDevToolsExtension(`${extensionDir}/${id}/${version}`)
}

app.on('ready', createWindow);