update web_components

pkg/web_components/README.md

 # Web Components
 
 This package has the polyfills for
 [Shadow DOM](http://www.polymer-project.org/platform/shadow-dom.html),
 [Custom Elements](http://www.polymer-project.org/platform/custom-elements.html),
 and [HTML Imports](http://www.polymer-project.org/platform/html-imports.html).
 
 These features exist in dart:html, for example
 [Element.reateShadowRoot](https://api.dartlang.org/apidocs/channels/stable/#dart-dom-html.Element@id_createShadowRoot)
 and [Document.register](https://api.dartlang.org/apidocs/channels/stable/#dart-dom-html.HtmlDocument@id_register).
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 shadow roots. It provides a method of establishing and maintaining functional
 boundaries between DOM trees and how these trees interact with each other within
 a document, thus enabling better functional encapsulation within the DOM.
 
 See the Polymer [Shadow DOM page](http://www.polymer-project.org/platform/shadow-dom.html)
 for more information.
 
 
 ## Hacking on this package
 
-*NOTE*: Currently we use
-[a patched version of CustomElements](https://github.com/dart-lang/CustomElements/tree/blink_tests).
-This is to get polyfilled behavior closer to native.
-See [this pull request](https://github.com/Polymer/CustomElements/pull/97) for
-more information. It is not required to use these changes; platform.js from
-https://polymer-project.org will work just as well, but it will have less error
-checking.
-
 To rebuild platform.js:
 
 ```bash
 # Make a directory like ~/src/polymer
 mkdir ~/src/polymer
 cd ~/src/polymer
 git clone https://github.com/polymer/tools
 
 # Sync polymer repositories
 ./tools/bin/pull-all-polymer.sh
 
 # If you don't have "npm", get it here: http://nodejs.org
 cd platform-dev
 npm install
 grunt minify audit
 cd build
 
 # Copy the build output to your Dart source tree
 cp build.log platform* ~/dart/dart/pkg/web_components/lib
 ```