Make cloneNode() throw for ShadowRoot objects

See WICG/webcomponents#393 for context.

dom.bs

@@ -3569,9 +3569,16 @@ dom-Range-extractContents, dom-Range-cloneContents -->
  <li>Return <var>copy</var>.
 </ol>
 
-The <dfn method for=Node><code>cloneNode(<var>deep</var>)</code></dfn> method, when
-invoked, must return a <a lt="clone a node">clone</a> of the <a>context object</a>, with
-the <i>clone children flag</i> set if <var>deep</var> is true.
+<p>The <dfn method for=Node><code>cloneNode(<var>deep</var>)</code></dfn> method, when
+invoked, must run these steps:
+
+<ol>
+ <li><p>If <a>context object</a> is a <a>shadow root</a>, <a>throw</a> a {{NotSupportedError}}
+ exception.
+
+ <li><p>Return a <a lt="clone a node">clone</a> of the <a>context object</a>, with the
+ <i>clone children flag</i> set if <var>deep</var> is true.
+</ol>
 
 A <a>node</a> <var>A</var>
 <dfn export for=Node id=concept-node-equals>equals</dfn> a <a>node</a>

dom.html

@@ -2043,8 +2043,13 @@ <h3 class="heading settled" data-level="4.4" id="interface-node"><span class="se
      <li>Return <var>copy</var>. 
     </ol>
     <p>The <dfn class="idl-code" data-dfn-for="Node" data-dfn-type="method" data-export="" data-lt="cloneNode(deep)|cloneNode()" id="dom-node-clonenode"><code>cloneNode(<var>deep</var>)</code><a class="self-link" href="#dom-node-clonenode"></a></dfn> method, when
-invoked, must return a <a data-link-type="dfn" href="#concept-node-clone">clone</a> of the <a data-link-type="dfn" href="#context-object">context object</a>, with
-the <i>clone children flag</i> set if <var>deep</var> is true.</p>
+invoked, must run these steps: </p>
+    <ol>
+     <li>
+      <p>If <a data-link-type="dfn" href="#context-object">context object</a> is a <a data-link-type="dfn" href="https://w3c.github.io/webcomponents/spec/shadow/#dfn-shadow-root">shadow root</a>, <a data-link-type="dfn" href="https://heycam.github.io/webidl/#dfn-throw">throw</a> a <code class="idl"><a data-link-type="idl" href="https://heycam.github.io/webidl/#notsupportederror">NotSupportedError</a></code> exception. </p>
+     <li>
+      <p>Return a <a data-link-type="dfn" href="#concept-node-clone">clone</a> of the <a data-link-type="dfn" href="#context-object">context object</a>, with the <i>clone children flag</i> set if <var>deep</var> is true. </p>
+    </ol>
     <p>A <a data-link-type="dfn" href="#concept-node">node</a> <var>A</var> <dfn data-dfn-for="Node" data-dfn-type="dfn" data-export="" id="concept-node-equals">equals<a class="self-link" href="#concept-node-equals"></a></dfn> a <a data-link-type="dfn" href="#concept-node">node</a> <var>B</var> if all of the following conditions are true:</p>
     <ul>
      <li><var>A</var> and <var>B</var>’s <code class="idl"><a data-link-type="idl" href="#dom-node-nodetype">nodeType</a></code> attribute value is identical.