Add support for not including platform.js in build output

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:analyzer/src/generated/ast.dart';
@@ skipping 75 matching lines @@
 
   /// This will make a physical element appear on the page showing build logs.
   /// It will only appear when ![releaseMode] even if this is true.
   final bool injectBuildLogsInOutput;
 
   /// True to run liner on all html files before starting other phases.
   // TODO(jmesserly): instead of this flag, we should only run linter on
   // reachable (entry point+imported) html if deploying. See dartbug.com/17199.
   final bool lint;
 
+  /// This will automatically inject `platform.js` from the `web_components`
+  /// package in all entry points, if it is not already included.
+  final bool injectPlatformJs;
+
   TransformOptions({entryPoints, this.inlineStylesheets,
       this.contentSecurityPolicy: false, this.directlyIncludeJS: true,
       this.releaseMode: true, this.lint: true,
-      this.injectBuildLogsInOutput: false})
+      this.injectBuildLogsInOutput: false, this.injectPlatformJs: 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 113 matching lines @@
 /// Returns true if this is a valid custom element name. See:
 /// <http://w3c.github.io/webcomponents/spec/custom/#dfn-custom-element-type>
 bool isCustomTagName(String name) {
   if (name == null || !name.contains('-')) return false;
   return !invalidTagNames.containsKey(name);
 }
 
 /// Regex to split names in the 'attributes' attribute, which supports 'a b c',
 /// 'a,b,c', or even 'a b,c'. This is the same as in `lib/src/declaration.dart`.
 final ATTRIBUTES_REGEX = new RegExp(r'\s|,');