Add referrerpolicy to <layer>'s content attributes

spec/index.html

@@ -446,6 +446,7 @@ <h5 id="the-layer-element"><em><span class="secno">4.1.2</span> The <dfn><code>l
    <dd id="attr-layer-label"><em><code><a href="#attr-layer-label">label</a></code> - String label for the layer in the layer control, if displayed</em></dd>
    <dd id="attr-layer-checked"><em><code><a href="#attr-layer-checked">checked</a></code> - Layer on/off status</em></dd>
    <dd id="attr-layer-hidden"><em><code><a href="#attr-layer-hidden">hidden</a></code> - Visibility status of the layer in the layer control</em></dd>
+   <dd id="attr-layer-referrerpolicy"><em><code><a href="#attr-layer-referrerpolicy">referrerpolicy</a></code> - <a href="https://w3c.github.io/webappsec-referrer-policy/#referrer-policy">Referrer policy</a> for <a href="https://fetch.spec.whatwg.org/#concept-fetch">fetches</a> initiated by the element</em></dd>
   <dt><span>Tag omission in text/html</span>:</dt>
    <dd>Neither tag is omissible</dd>
    <dt>Allowed <a target="_blank" href="https://www.w3.org/TR/2014/REC-html5-20141028/dom.html#aria-role-attribute">ARIA role attribute</a> values:</dt>
@@ -461,6 +462,7 @@ <h5 id="the-layer-element"><em><span class="secno">4.1.2</span> The <dfn><code>l
   <em> readonly attribute boolean <a href="#attr-layer-disabled">disabled</a>;</em>
   <em>          attribute boolean <a href="#attr-layer-hidden">hidden</a>;</em>
   <em> readonly attribute <a href="#legendlink">LegendLink[]</a> legendLinks;</em>
+  <em>          attribute DOMString <a href="#attr-layer-referrerpolicy">referrerpolicy</a>;</em>
 };
 
 interface <dfn id="legendlink">LegendLink</dfn> {