Add a build filter (only necessary HTML files are emitted) and logic to use .min.js

pkg/polymer/lib/src/build/common.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /** Common methods used by transfomers. */
 library polymer.src.build.common;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
@@ skipping 44 matching lines @@
   /**
    * True to include the compiled JavaScript directly from the HTML page.
    * If enabled this will remove "packages/browser/dart.js" and replace
    * `type="application/dart"` scripts with equivalent *.dart.js files.
    *
    * If [contentSecurityPolicy] enabled, this will reference files
    * named *.dart.precompiled.js.
    */
   final bool directlyIncludeJS;
 
+  /**
+   * Run transformers to create a releasable app. For example, include the
+   * minified versions of the polyfills rather than the debug versions.
+   */
+  final bool releaseMode;
+
   TransformOptions({entryPoints, this.contentSecurityPolicy: false,
-      this.directlyIncludeJS: true})
+      this.directlyIncludeJS: true, this.releaseMode: true})
       : entryPoints = entryPoints == null ? null
           : entryPoints.map(_systemToAssetPath).toList();
 
   /** Whether an asset with [id] is an entry point HTML file. */
   bool isHtmlEntryPoint(AssetId id) {
     if (id.extension != '.html') return false;
 
     // Note: [id.path] is a relative path from the root of a package.
     if (entryPoints == null) {
       return id.path.startsWith('web/') || id.path.startsWith('test/');
@@ skipping 101 matching lines @@
   return builder.relative(builder.join('/', id.path),
       from: builder.join('/', builder.dirname(sourceId.path)));
 }
 
 
 /** Convert system paths to asset paths (asset paths are posix style). */
 String _systemToAssetPath(String assetPath) {
   if (path.Style.platform != path.Style.windows) return assetPath;
   return path.posix.joinAll(path.split(assetPath));
 }