Apply a source map to a vinyl file, merging it with preexisting source maps.
var applySourceMap = require('vinyl-sourcemaps-apply');
applySourceMap(vinylFile, sourceMap);
var through = require('through2');
var applySourceMap = require('vinyl-sourcemaps-apply');
var myTransform = require('myTransform');
module.exports = function(options) {
  function transform(file, encoding, callback) {
    // generate source maps if plugin source-map present
    if (file.sourceMap) {
      options.makeSourceMaps = true;
    }
    // do normal plugin logic
    var result = myTransform(file.contents, options);
    file.contents = new Buffer(result.code);
    // apply source map to the chain
    if (file.sourceMap) {
      applySourceMap(file, result.map);
    }
    this.push(file);
    callback();
  }
  return through.obj(transform);
};