Live-reload for Polymer Chrome Apps - http://codingwithgerwin.blogspot.com/2015/07/live-reload-for-polymer-chrome-apps.html

gulp-batch.js

gulp.watch(['dev/**'], $.batch(function (events, cb) {
  var paths = [];
  events.on('data', function (evt) {
    paths.push(evt.path);
  }).on('end', function () {
    lr.changed({
      body: {
        files: paths
      }
    });
    cb();
  });
}));

gulp-build-dev.js

gulp.task('dev', ['build'],  function () {
  var lr = tinylr();
  lr.listen(35729);

  gulp.watch(['app/**'], ['build']);

  gulp.watch(['dist/**'], function (evt) {
    lr.changed({
      body: {
        files: [evt.path]
      }
    });
  });
});

gulp-build.js

gulp.task('build', function (cb) {
  runSequence(
    ['copy', 'styles'],
    'elements',
    ['jshint', 'images', 'html'],
    'vulcanize',
    cb
  );
});

gulp-crisper.js

gulp.task('crisper', function () {
  var elements = gulp.src(['app/elements/**/*.html'])
    .pipe($.crisper())
    .pipe(gulp.dest('dev/elements'));

  var bower = gulp.src(['bower_components/**/*.html'])
    .pipe($.crisper())
    .pipe(gulp.dest('dev/bower_components'));

  return merge(bower, elements)
    .pipe($.size({title: 'crisper'}));
});

gulp-dev-build.js

gulp.task('dev', ['clean:dev'], function (cb) {
  runSequence(
    ['copy:app', 'copy:elements', 'styles'],
    'elements',
    ['jshint', 'images'],
    'crisper',
    'watch',
    cb
  );
});

gulp-reload.js

var gulp = require('gulp');
var tinylr = require('tiny-lr');

gulp.task('dev', function () {
  var lr = tinylr();
  lr.listen(35729);
  gulp.watch(['**.{js,css,html}'], function (evt) {
    lr.changed({
      body: {
        files: [evt.path]
      }
    });
  });
});

gulp-vulcocrisp.js

gulp.task('vulcanize', function () {
  var DEST_DIR = 'dist/elements';

  return gulp.src('dist/elements/elements.vulcanized.html')
    .pipe($.vulcanize({
      stripComments: true,
      inlineCss: true,
      inlineScripts: true
    }))
    .pipe($.crisper())
    .pipe(gulp.dest(DEST_DIR))
    .pipe($.size({title: 'vulcanize'}));
});

gulp-watch.js

gulp.task('watch', function () {
  var lr = tinylr();
  lr.listen(35729);

  gulp.watch(['app/*'], ['copy:app']);
  gulp.watch(['app/**/*.js'], ['jshint', 'copy:app']);
  gulp.watch(['app/styles/**/*.css'], ['styles']);
  gulp.watch(['app/elements/**/*.css'], ['elements']);
  gulp.watch(['app/elements/**/*.html'], function () {
    runSequence(
      'copy:elements',
      'crisper'
    );
  });
  gulp.watch(['app/images/**/*'], ['images']);

  gulp.watch(['dev/**'], function (evt) {
    lr.changed({
      body: {
        files: [evt.path]
      }
    });
  });
});

gulpfile.js

'use strict';

// Include Gulp & Tools We'll Use
var gulp = require('gulp');
var $ = require('gulp-load-plugins')();
var del = require('del');
var runSequence = require('run-sequence');
var merge = require('merge-stream');
var path = require('path');
var tinylr = require('tiny-lr');

var destDir = 'dist';

var AUTOPREFIXER_BROWSERS = [
  'chrome >= 34'
];

var styleTask = function (stylesPath, srcs) {
  return gulp.src(srcs.map(function(src) {
      return path.join('app', stylesPath, src);
    }))
    .pipe($.changed(stylesPath, {extension: '.css'}))
    .pipe($.autoprefixer(AUTOPREFIXER_BROWSERS))
    .pipe(gulp.dest('.tmp/' + stylesPath))
    .pipe($.if('*.css', $.cssmin()))
    .pipe(gulp.dest(destDir + '/' + stylesPath))
    .pipe($.size({title: stylesPath}));
};

// Compile and Automatically Prefix Stylesheets
gulp.task('styles', function () {
  return styleTask('styles', ['**/*.css']);
});

gulp.task('elements', function () {
  return styleTask('elements', ['**/*.css']);
});

// Lint JavaScript
gulp.task('jshint', function () {
  return gulp.src([
      'app/scripts/**/*.js',
      'app/elements/**/*.js',
      'app/elements/**/*.html'
    ])
    .pipe($.jshint.extract()) // Extract JS from .html files
    .pipe($.jshint())
    .pipe($.jshint.reporter('jshint-stylish'))
    .pipe($.jshint.reporter('fail'));
});

// Optimize Images
gulp.task('images', function () {
  return gulp.src('app/images/**/*')
    .pipe($.cache($.imagemin({
      progressive: true,
      interlaced: true
    })))
    .pipe(gulp.dest(destDir + '/images'))
    .pipe($.size({title: 'images'}));
});

// Copy All Files At The Root Level (app)
gulp.task('copy', function () {
  var app = gulp.src([
    'app/*',
    '!app/test',
    '!app/precache.json'
  ], {
    dot: true
  }).pipe(gulp.dest(destDir));

  var bower = gulp.src([
    'bower_components/**/*'
  ]).pipe(gulp.dest(destDir + '/bower_components'));

  var elements = gulp.src(['app/elements/**/*.html'])
    .pipe(gulp.dest(destDir + '/elements'));

  var vulcanized = gulp.src(['app/elements/elements.html'])
    .pipe($.rename('elements.vulcanized.html'))
    .pipe(gulp.dest(destDir + '/elements'));

  return merge(app, bower, elements, vulcanized)
    .pipe($.size({title: 'copy'}));
});

// Scan Your HTML For Assets & Optimize Them
gulp.task('html', function () {
  var assets = $.useref.assets({searchPath: ['.tmp', 'app', 'dist']});

  return gulp.src(['app/**/*.html', '!app/{elements,test}/**/*.html'])
    // Replace path for vulcanized assets
    .pipe($.if('*.html', $.replace(
      'elements/elements.html',
      'elements/elements.vulcanized.html'
    )))
    .pipe(assets)
    // Concatenate And Minify JavaScript
    .pipe($.if('*.js', $.uglify({preserveComments: 'some'})))
    // Concatenate And Minify Styles
    // In case you are still using useref build blocks
    .pipe($.if('*.css', $.cssmin()))
    .pipe(assets.restore())
    .pipe($.useref())
    // Minify Any HTML
    .pipe($.if('*.html', $.minifyHtml({
      quotes: true,
      empty: true,
      spare: true
    })))
    // Output Files
    .pipe(gulp.dest(destDir))
    .pipe($.size({title: 'html'}));
});

// Vulcanize imports
gulp.task('vulcanize', function () {
  var DEST_DIR = destDir + '/elements';

  return gulp.src(destDir + '/elements/elements.vulcanized.html')
    .pipe($.vulcanize({
      dest: DEST_DIR,
      strip: true,
      inlineCss: true,
      inlineScripts: false
    }))
    .pipe($.crisper())
    .pipe(gulp.dest(DEST_DIR))
    .pipe($.size({title: 'vulcanize'}));
});

gulp.task('copy:app', function() {
  return gulp.src([
    'app/*',
    'app/**/*.js',
    '!app/test',
    '!app/precache.json'
  ], {
    dot: true
  }).pipe(gulp.dest(destDir));
});

gulp.task('dev:elements', function() {
  return gulp.src(['app/elements/**/*'])
    .pipe($.if('*.html', $.crisper()))
    .pipe(gulp.dest(destDir + '/elements'))
    .pipe($.size({title: 'dev:elements'}));
});

gulp.task('dev:bower', function() {
  return gulp.src(['bower_components/**/*'])
    .pipe($.if('*.html', $.crisper()))
    .pipe(gulp.dest(destDir + '/bower_components'))
    .pipe($.size({title: 'dev:bower'}));
});

// Clean Output Directory
gulp.task('clean', del.bind(null, ['.tmp', 'dist']));

// Clean Output Directory
gulp.task('clean:dev', del.bind(null, ['.tmp', 'dev']));

// Clear cache (used by imagemin)
gulp.task('clearcache', function (cb) {
  return $.cache.clearAll(cb);
});

gulp.task('watch', function () {
  var lr = tinylr();
  lr.listen(35729);

  gulp.watch(['app/*'], ['copy:app']);
  gulp.watch(['app/**/*.js'], ['jshint', 'copy:app']);
  gulp.watch(['app/styles/**/*.css'], ['styles']);
  gulp.watch(['app/elements/**'], ['dev:elements']);
  gulp.watch(['bower_components/**'], ['dev:bower']);
  gulp.watch(['app/images/**/*'], ['images']);

  gulp.watch(['dev/**'], $.batch(function (events, cb) {
    var paths = [];
    events.on('data', function (evt) {
      paths.push(evt.path);
    }).on('end', function () {
      lr.changed({
        body: {
          files: paths
        }
      });
      cb();
    });
  }));
});

gulp.task('dev', ['clean:dev', 'clearcache'], function (cb) {
  destDir = 'dev';
  runSequence(
    ['copy:app', 'styles'],
    ['dev:elements', 'dev:bower'],
    ['jshint', 'images'],
    'watch',
    cb
  );
});

// Build Production Files, the Default Task
gulp.task('default', ['clean', 'clearcache'], function (cb) {
  runSequence(
    ['copy', 'styles'],
    'elements',
    ['jshint', 'images', 'html'],
    'vulcanize',
    cb
  );
});

@jarrodek I've added the full gulpfile that I'm currently using to this gist. Some changes since I wrote the article but the idea is the same.