old_contents: /**
   * Copyright 2016 Google Inc. All Rights Reserved.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  var gulp = require('gulp');
  var rename = require('gulp-rename');
  var uglify = require('gulp-uglify');
  var sourcemaps = require('gulp-sourcemaps');
  var mochaPhantomJS = require('gulp-mocha-phantomjs');
  var jshint = require('gulp-jshint');
  var concat = require('gulp-concat');
  
  var SRC_FILE = 'stackdriver-errors.js';
  var DEST = 'dist/';
  
  var dependencies = [
      './node_modules/stacktrace-js/dist/stacktrace-with-promises-and-json-polyfills.js',
  ];
  
  gulp.task('lint', function() {
    return gulp.src(SRC_FILE)
      .pipe(jshint())
      .pipe(jshint.reporter('default'));
  });
  
  gulp.task('test', function () {
      return gulp
      .src('test/test.html')
      .pipe(mochaPhantomJS({reporter: 'spec'}));
  });
  
  gulp.task('dist', function() {
    return gulp.src(dependencies.concat(SRC_FILE))
      .pipe(sourcemaps.init())
      .pipe(concat(SRC_FILE.replace('.js', '-concat.js')))
      // This will output the non-minified version
      .pipe(gulp.dest(DEST))
      // This will minify and rename to stackdriver-errors.min.js
      .pipe(uglify())
      .pipe(rename({ extname: '.min.js' }))
      .pipe(sourcemaps.write('maps'))
      .pipe(gulp.dest(DEST));
  });
  
  gulp.task('min-demo', function() {
    return gulp.src('demo/demo.js')
      .pipe(sourcemaps.init())
      .pipe(uglify())
      .pipe(rename({ extname: '.min.js' }))
      .pipe(sourcemaps.write('maps'))
      .pipe(gulp.dest('demo'));
  });
  
  gulp.task('default', ['lint', 'test']);
  
new_contents: /**
   * Copyright 2016 Google Inc. All Rights Reserved.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  var gulp = require('gulp');
  var rename = require('gulp-rename');
  var uglify = require('gulp-uglify');
  var sourcemaps = require('gulp-sourcemaps');
  var mochaPhantomJS = require('gulp-mocha-phantomjs');
  var jshint = require('gulp-jshint');
  var concat = require('gulp-concat');
  
  var SRC_FILE = 'stackdriver-errors.js';
  var DEST = 'dist/';
  
  var dependencies = [
      './node_modules/stacktrace-js/dist/stacktrace-with-promises-and-json-polyfills.js',
  ];
  
  gulp.task('lint', function() {
    return gulp.src(SRC_FILE)
      .pipe(jshint())
      .pipe(jshint.reporter('default'));
  });
  
  gulp.task('test', function () {
      return gulp
      .src('test/test.html')
      .pipe(mochaPhantomJS({reporter: 'spec'}));
  });
  
  gulp.task('dist', function() {
    return gulp.src(dependencies.concat(SRC_FILE))
      .pipe(sourcemaps.init({ loadMaps: true }))
      .pipe(concat(SRC_FILE.replace('.js', '-concat.js')))
      // This will output the non-minified version
      .pipe(gulp.dest(DEST))
      // This will minify and rename to stackdriver-errors.min.js
      .pipe(uglify())
      .pipe(rename({ extname: '.min.js' }))
      .pipe(sourcemaps.write('maps'))
      .pipe(gulp.dest(DEST));
  });
  
  gulp.task('min-demo', function() {
    return gulp.src('demo/demo.js')
      .pipe(sourcemaps.init())
      .pipe(uglify())
      .pipe(rename({ extname: '.min.js' }))
      .pipe(sourcemaps.write('maps'))
      .pipe(gulp.dest('demo'));
  });
  
  gulp.task('default', ['lint', 'test']);
  
subject: Read dependency sourcemaps on build (#47)