Add Polymer iron-image to Chromium checkout.

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

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+[![Build Status](https://travis-ci.org/PolymerElements/iron-image.svg?branch=master)](https://travis-ci.org/PolymerElements/iron-image)
+
+_[Demo and API Docs](https://elements.polymer-project.org/elements/iron-image)_
+
+
+##&lt;iron-image&gt;
+
+`iron-image` is an element for displaying an image that provides useful sizing and
+preloading options not found on the standard `<img>` tag.
+
+The `sizing` option allows the image to be either cropped (`cover`) or
+letterboxed (`contain`) to fill a fixed user-size placed on the element.
+
+The `preload` option prevents the browser from rendering the image until the
+image is fully loaded.  In the interim, either the element's CSS `background-color`
+can be be used as the placeholder, or the `placeholder` property can be
+set to a URL (preferably a data-URI, for instant rendering) for an
+placeholder image.
+
+The `fade` option (only valid when `preload` is set) will cause the placeholder
+image/color to be faded out once the image is rendered.
+
+Examples:
+
+  Basically identical to `<img src="...">` tag:
+
+```html
+<iron-image src="http://lorempixel.com/400/400"></iron-image>
+```
+
+  Will letterbox the image to fit:
+
+```html
+<iron-image style="width:400px; height:400px;" sizing="contain"
+  src="http://lorempixel.com/600/400"></iron-image>
+```
+
+  Will crop the image to fit:
+
+```html
+<iron-image style="width:400px; height:400px;" sizing="cover"
+  src="http://lorempixel.com/600/400"></iron-image>
+```
+
+  Will show light-gray background until the image loads:
+
+```html
+<iron-image style="width:400px; height:400px; background-color: lightgray;"
+  sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image>
+```
+
+  Will show a base-64 encoded placeholder image until the image loads:
+
+```html
+<iron-image style="width:400px; height:400px;" placeholder="data:image/gif;base64,..."
+  sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image>
+```
+
+  Will fade the light-gray background out once the image is loaded:
+
+```html
+<iron-image style="width:400px; height:400px; background-color: lightgray;"
+  sizing="cover" preload fade src="http://lorempixel.com/600/400"></iron-image>
+```
+
+| Custom property | Description | Default |
+| --- | --- | --- |
+| `--iron-image-placeholder` | Mixin applied to #placeholder | `{}` |
+| `--iron-image-width` | Sets the width of the wrapped image | `auto` |
+| `--iron-image-height` | Sets the height of the wrapped image | `auto` |
+
+