[pinpoint] Add iron-form and paper-checkbox to polymer components.

third_party/polymer/components/paper-checkbox/README.md

+[![Build status](https://travis-ci.org/PolymerElements/paper-checkbox.svg?branch=master)](https://travis-ci.org/PolymerElements/paper-checkbox)
+
+##<paper-checkbox>
+
+`paper-checkbox` is a [material design checkbox](https://www.google.com/design/spec/components/selection-controls.html#selection-controls-checkbox). 
+User can tap the checkbox to check or uncheck it. Usually you use checkboxes
+to allow user to select multiple options from a set. If you have a single
+ON/OFF option, avoid using a single checkbox and use `paper-toggle-button`
+instead.
+
+Example:
+<!---
+```
+<custom-element-demo>
+  <template>
+    <script src="../webcomponentsjs/webcomponents-lite.js"></script>
+    <link rel="import" href="paper-checkbox.html">
+    <style is="custom-style">
+      paper-checkbox {
+        font-family: 'Roboto', sans-serif;
+        margin: 24px;
+      }
+        
+      paper-checkbox:first-child {
+        --primary-color: #ff5722;
+      }
+      
+      paper-checkbox.styled {
+        align-self: center;
+        border: 1px solid var(--paper-green-200);
+        padding: 8px 16px;
+        --paper-checkbox-checked-color: var(--paper-green-500);
+        --paper-checkbox-checked-ink-color: var(--paper-green-500);
+        --paper-checkbox-unchecked-color: var(--paper-green-900);
+        --paper-checkbox-unchecked-ink-color: var(--paper-green-900);
+        --paper-checkbox-label-color: var(--paper-green-500);
+        --paper-checkbox-label-spacing: 0;
+        --paper-checkbox-margin: 8px 16px 8px 0;
+        --paper-checkbox-vertical-align: top;
+      }
+
+      paper-checkbox .subtitle {
+        display: block;
+        font-size: 0.8em;
+        margin-top: 2px;
+        max-width: 150px;
+      }
+    </style>
+    <next-code-block></next-code-block>
+  </template>
+</custom-element-demo>
+```
+-->
+```html
+<paper-checkbox checked>Checked</paper-checkbox>
+<paper-checkbox class="styled">
+  Checkbox
+  <span class="subtitle">
+    With a longer label
+  </span>
+</paper-checkbox>
+<paper-checkbox disabled>Disabled</paper-checkbox>
+```