[third_party] add polymer 1.2.3

polymer_1.2.3/bower_components/iron-collapse/README.md

+
+<!---
+
+This README is automatically generated from the comments in these files:
+iron-collapse.html
+
+Edit those files, and our readme bot will duplicate them over here!
+Edit this file, and the bot will squash your changes :)
+
+-->
+
+[![Build Status](https://travis-ci.org/PolymerElements/iron-collapse.svg?branch=master)](https://travis-ci.org/PolymerElements/iron-collapse)
+
+_[Demo and API Docs](https://elements.polymer-project.org/elements/iron-collapse)_
+
+
+##&lt;iron-collapse&gt;
+
+
+`iron-collapse` creates a collapsible block of content.  By default, the content
+will be collapsed.  Use `opened` or `toggle()` to show/hide the content.
+
+    <button on-click="toggle">toggle collapse</button>
+
+    <iron-collapse id="collapse">
+      <div>Content goes here...</div>
+    </iron-collapse>
+
+    ...
+
+    toggle: function() {
+      this.$.collapse.toggle();
+    }
+
+`iron-collapse` adjusts the height/width of the collapsible element to show/hide
+the content.  So avoid putting padding/margin/border on the collapsible directly,
+and instead put a div inside and style that.
+
+    <style>
+      .collapse-content {
+        padding: 15px;
+        border: 1px solid #dedede;
+      }
+    </style>
+
+    <iron-collapse>
+      <div class="collapse-content">
+        <div>Content goes here...</div>
+      </div>
+    </iron-collapse>
+
+