Make <link rel="stylesheet"> work inside shadow trees

Fixes WICG/webcomponents#530.

source

@@ -2129,16 +2129,27 @@ a.setAttribute('href', 'http://example.com/'); // change the content attribute d
 
   <p>A <dfn id="insert-an-element-into-a-document" data-x="node is inserted into a document">node is
   inserted into a document</dfn> when the <span data-x="concept-node-insert-ext">insertion
-  steps</span> are invoked with it as argument and it is now <span>in a document tree</span>.
+  steps</span> are invoked with it as the argument and it is now <span>in a document tree</span>.
   Analogously, a <dfn id="remove-an-element-from-a-document" data-x="node is removed from a
   document">node is removed from a document</dfn> when the <span
-  data-x="concept-node-remove-ext">removing steps</span> are invoked with it as argument and it is
-  now no longer <span>in a document tree</span>.</p>
+  data-x="concept-node-remove-ext">removing steps</span> are invoked with it as the argument and it
+  is now no longer <span>in a document tree</span>.</p>
 
   <p>A node <dfn>becomes connected</dfn> when the <span data-x="concept-node-insert-ext">insertion
-  steps</span> are invoked with it as argument and it is now <span>connected</span>. Analogously, a
-  node <dfn>becomes disconnected</dfn> when the <span data-x="concept-node-remove-ext">removing
-  steps</span> are invoked with it as argument and it is now no longer <span>connected</span>.</p>
+  steps</span> are invoked with it as the argument and it is now <span>connected</span>.
+  Analogously, a node <dfn>becomes disconnected</dfn> when the <span
+  data-x="concept-node-remove-ext">removing steps</span> are invoked with it as the argument and it
+  is now no longer <span>connected</span>.</p>
+
+  <p>A node is <dfn>browsing-context connected</dfn> when it is <span>connected</span> and its <span
+  data-x="shadow-including root">shadow-including root</span> has a <span
+  data-x="concept-document-bc">browsing context</span>. A node <dfn>becomes browsing-context
+  connected</dfn> when the <span data-x="concept-node-insert-ext">insertion steps</span> are invoked
+  with it as the argument and it is now <span>browsing-context connected</span>. A node <dfn>becomes
+  browsing-context disconnected</dfn> either when the <span
+  data-x="concept-node-remove-ext">removing steps</span> are invoked with it as the argument and it
+  is now no longer <span>browsing-context connected</span>, or when its <span>shadow-including
+  root</span> no longer has a <span data-x="concept-document-bc">browsing context</span>.
 
 
   <h4>Scripting</h4>
@@ -3139,7 +3150,7 @@ a.setAttribute('href', 'http://example.com/'); // change the content attribute d
 
      <li>The <dfn data-noexport="" data-x-href="https://dom.spec.whatwg.org/#concept-tree">tree</dfn> and <dfn data-noexport="" data-x-href="https://dom.spec.whatwg.org/#concept-shadow-tree">shadow tree</dfn> concepts</li>
      <li>The <dfn data-x-href="https://dom.spec.whatwg.org/#concept-tree-order">tree order</dfn> and <dfn data-x-href="https://dom.spec.whatwg.org/#concept-shadow-including-tree-order">shadow-including tree order</dfn> concepts</li>
-     <li>The <dfn data-noexport="" data-x-href="https://dom.spec.whatwg.org/#concept-tree-root">root</dfn> concept</li>
+     <li>The <dfn data-x-href="https://dom.spec.whatwg.org/#concept-tree-root">root</dfn> and <dfn data-x-href="https://dom.spec.whatwg.org/#concept-shadow-including-root">shadow-including root</dfn> concepts</li>
      <li>The <dfn data-x-href="https://dom.spec.whatwg.org/#concept-tree-inclusive-ancestor">inclusive ancestor</dfn> and <dfn data-x-href="https://dom.spec.whatwg.org/#concept-shadow-including-descendant">shadow-including descendant</dfn> concepts</li>
      <li>The <dfn data-noexport="" data-x-href="https://dom.spec.whatwg.org/#document-element">document element</dfn> concept</li>
      <li>The <dfn data-x-href="https://dom.spec.whatwg.org/#in-a-document-tree">in a document tree</dfn>, <dfn data-x-href="https://dom.spec.whatwg.org/#in-a-document">in a document</dfn> (legacy), and <dfn data-x-href="https://dom.spec.whatwg.org/#connected">connected</dfn> concepts</li>
@@ -23272,39 +23283,37 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
   <ul>
 
    <li><p>When the <span>external resource link</span> is created on a <code>link</code> element
-   that is already <span>in a document</span> that has a <span data-x="concept-document-bc">browsing
-   context</span>.</p></li>
+   that is already <span>browsing-context connected</span>.</p></li>
    <!-- e.g. rel="" changed, href="" set... -->
 
-   <li><p>When the <span>external resource link</span>'s <code>link</code> element is <span
-   data-x="node is inserted into a document">inserted into a document</span> that has a <span
-   data-x="concept-document-bc">browsing context</span>.</p></li>
+   <li><p>When the <span>external resource link</span>'s <code>link</code> element <span>becomes
+   browsing-context connected</span>.</p></li>
 
    <li><p>When the <code data-x="attr-link-href">href</code> attribute of the <code>link</code>
-   element of an <span>external resource link</span> that is already <span>in a document</span> that
-   has a <span data-x="concept-document-bc">browsing context</span> is changed.</p></li>
+   element of an <span>external resource link</span> that is already <span>browsing-context
+   connected</span> is changed.</p></li>
    <!-- http://software.hixie.ch/utilities/js/live-dom-viewer/saved/2588 -->
 
    <li><p>When the <code data-x="attr-link-crossorigin">crossorigin</code> attribute of the
    <code>link</code> element of an <span data-x="external resource link">external resource
-   link</span> that is already <span>in a document</span> that has a <span
-   data-x="concept-document-bc">browsing context</span> is set, changed, or removed.</p></li>
+   link</span> that is already <span>browsing-context connected</span> is set, changed, or
+   removed.</p></li>
 
    <li><p>When the <code data-x="attr-link-type">type</code> attribute of the <code>link</code>
-   element of an <span>external resource link</span> that is already <span>in a document</span> that
-   has a <span data-x="concept-document-bc">browsing context</span> is set or changed to a value
-   that does not or no longer matches the <span data-x="Content-Type">Content-Type metadata</span>
-   of the previous obtained external resource, if any.</p></li>
+   element of an <span>external resource link</span> that is already <span>browsing-context
+   connected</span> is set or changed to a value that does not or no longer matches the <span
+   data-x="Content-Type">Content-Type metadata</span> of the previous obtained external resource, if
+   any.</p></li>
 
    <li><p>When the <code data-x="attr-link-type">type</code> attribute of the <code>link</code>
-   element of an <span>external resource link</span> that is already <span>in a document</span> that
-   has a <span data-x="concept-document-bc">browsing context</span>, but was previously not obtained
-   due to the <code data-x="attr-link-type">type</code> attribute specifying an unsupported type, is
-   set, removed, or changed.</p></li>
-
-   <li><p>When the <span>external resource link</span> changes from being <span data-x="the link is
-   an alternative stylesheet">an alternative stylesheet</span> to not being one, or vice
-   versa.</p></li>
+   element of an <span>external resource link</span> that is already <span>browsing-context
+   connected</span>, but was previously not obtained due to the <code
+   data-x="attr-link-type">type</code> attribute specifying an unsupported type, is set, removed, or
+   changed.</p></li>
+
+   <li><p>When the <span>external resource link</span> that is already <span>browsing-context
+   connected</span> changes from being <span data-x="the link is an alternative stylesheet">an
+   alternative stylesheet</span> to not being one, or vice versa.</p></li>
 
   </ul>