Add Polymer iron-image to Chromium checkout.

third_party/polymer/v1_0/components-chromium/iron-icons/README.md

 
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 [![Build Status](https://travis-ci.org/PolymerElements/iron-icons.svg?branch=master)](https://travis-ci.org/PolymerElements/iron-icons)
 
 _[Demo and API Docs](https://elements.polymer-project.org/elements/iron-icons)_
 
+
+##&lt;iron-icons&gt;
+
+`iron-icons` is a utitliy import that includes the definition for the `iron-icon` element, `iron-iconset-svg` element, as well as an import for the default icon set.
+
+The `iron-icons` directory also includes imports for additional icon sets that can be loaded into your project.
+
+Example loading icon set:
+
+```html
+<link rel="import" href="../iron-icons/maps-icons.html">
+```
+
+To use an icon from one of these sets, first prefix your `iron-icon` with the icon set name, followed by a colon, ":", and then the icon id.
+
+Example using the directions-bus icon from the maps icon set:
+
+```html
+<iron-icon icon="maps:directions-bus"></iron-icon>
+```
+
+See [iron-icon](#iron-icon) for more information about working with icons.
+
+See [iron-iconset](#iron-iconset) and [iron-iconset-svg](#iron-iconset-svg) for more information about how to create a custom iconset.
+
+