no longer require entry points to be specified in the build.dart file

pkg/polymer/lib/transformer.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.
 
 /// Transfomer used for pub-serve and pub-deploy.
 library polymer.transformer;
 
 import 'package:barback/barback.dart';
 import 'package:observe/transformer.dart';
 import 'package:path/path.dart' as path;
@@ skipping 27 matching lines @@
 
 TransformOptions _parseSettings(BarbackSettings settings) {
   var args = settings.configuration;
   bool releaseMode = settings.mode == BarbackMode.RELEASE;
   bool jsOption = args['js'];
   bool csp = args['csp'] == true; // defaults to false
   bool lint = args['lint'] != false; // defaults to true
   bool injectBuildLogs =
       !releaseMode && args['inject_build_logs_in_output'] != false;
   return new TransformOptions(
-      entryPoints: _readEntrypoints(args['entry_points']),
+      entryPoints: readEntrypoints(args['entry_points']),
       inlineStylesheets: _readInlineStylesheets(args['inline_stylesheets']),
       directlyIncludeJS: jsOption == null ? releaseMode : jsOption,
       contentSecurityPolicy: csp,
       releaseMode: releaseMode,
       lint: lint,
       injectBuildLogsInOutput: injectBuildLogs);
 }
 
-_readEntrypoints(value) {
+readEntrypoints(value) {
   if (value == null) return null;
   var entryPoints = [];
   bool error;
   if (value is List) {
     entryPoints = value;
     error = value.any((e) => e is! String);
   } else if (value is String) {
     entryPoints = [value];
     error = false;
   } else {
@@ skipping 54 matching lines @@
     [new ImportInliner(options)],
     [new ObservableTransformer()],
     [new ScriptCompactor(options, sdkDir: sdkDir)],
     [new PolyfillInjector(options)],
     [new BuildFilter(options)],
     [new BuildLogCombiner(options)],
   ]);
 }
 
 final RegExp _PACKAGE_PATH_REGEX = new RegExp(r'packages\/([^\/]+)\/(.*)');