old_contents: const webpack = require('webpack');
  
  const config = require('./webpack.config.base');
  
  module.exports = Object.assign({}, config, {
    plugins: config.plugins.concat([
      new webpack.DefinePlugin({
        'process.env': {
          NODE_ENV: JSON.stringify('development'),
        },
      }),
    ]),
  });
  
new_contents: const webpack = require('webpack');
  
  const config = require('./webpack.config.base');
  
  module.exports = Object.assign({}, config, {
    // See http://webpack.github.io/docs/configuration.html#devtool
    devtool: 'inline-source-map',
  
    plugins: config.plugins.concat([
      new webpack.DefinePlugin({
        'process.env': {
          NODE_ENV: JSON.stringify('development'),
        },
      }),
    ]),
  });
  
subject: Add missing source maps in dev mode