[MD settings] updating polymer to 1.1.13

third_party/polymer/v1_0/components-chromium/paper-dropdown-menu/README.md

 paper-dropdown-menu
 ===================
 
 `paper-dropdown-menu` is similar to a native browser select element.
+`paper-dropdown-menu` works with selectable content. The currently selected
+item is displayed in the control. If no item is selected, the `label` is
+displayed instead.
+The child element with the class `dropdown-content` will be used as the dropdown
+menu. It could be a `paper-menu` or element that triggers `iron-activate` when
+selecting its children.
+Example:
+
+    <paper-dropdown-menu label="Your favourite pastry">
+      <paper-menu class="dropdown-content">
+        <paper-item>Croissant</paper-item>
+        <paper-item>Donut</paper-item>
+        <paper-item>Financier</paper-item>
+        <paper-item>Madeleine</paper-item>
+      </paper-menu>
+    </paper-dropdown-menu>
+    
+This example renders a dropdown menu with 4 options.
+### Styling
+The following custom properties and mixins are also available for styling:
+
+Custom property | Description | Default
+----------------|-------------|----------
+`--paper-dropdown-menu` | A mixin that is applied to the element host | `{}`
+`--paper-dropdown-menu-disabled` | A mixin that is applied to the element host when disabled | `{}`
+`--paper-dropdown-menu-ripple` | A mixin that is applied to the internal ripple | `{}`
+`--paper-dropdown-menu-button` | A mixin that is applied to the internal menu button | `{}`
+`--paper-dropdown-menu-input` | A mixin that is applied to the internal paper input | `{}`
+`--paper-dropdown-menu-icon` | A mixin that is applied to the internal icon | `{}`
+You can also use any of the `paper-input-container` and `paper-menu-button`
+style mixins and custom properties to style the internal input and menu button
+respectively.