Meta: export WindowProxy for Shepherd

See whatwg/webidl#209 for motivation.

source

@@ -78412,12 +78412,12 @@ callback <dfn>FrameRequestCallback</dfn> = void (<span>DOMHighResTimeStamp</span
 
   <h3>The <code>WindowProxy</code> exotic object</h3>
 
-  <p>A <dfn><code>WindowProxy</code></dfn> is an exotic object that wraps a <code>Window</code>
-  ordinary object, indirecting most operations through to the wrapped object. Each
-  <span>browsing context</span> has an associated <code>WindowProxy</code> object. When the
-  <span>browsing context</span> is <span data-x="navigate">navigated</span>, the <code>Window</code>
-  object wrapped by the <span>browsing context</span>'s associated <code>WindowProxy</code> object
-  is changed.</p>
+  <p>A <dfn data-export="" data-dfn-type="interface"><code>WindowProxy</code></dfn> is an exotic
+  object that wraps a <code>Window</code> ordinary object, indirecting most operations through to
+  the wrapped object. Each <span>browsing context</span> has an associated <code>WindowProxy</code>
+  object. When the <span>browsing context</span> is <span data-x="navigate">navigated</span>, the
+  <code>Window</code> object wrapped by the <span>browsing context</span>'s associated
+  <code>WindowProxy</code> object is changed.</p>
 
   <p>There is no <code>WindowProxy</code> <span>interface object</span>.</p>