Execute <script> in shadow trees

This makes <script> elements work when used in shadow trees. The
beforescriptexecute and afterscriptexecute events won’t work, since
they are already disabled for modules and only makes sense together
with currentScript, which cannot be made to work for shadow scripts.
See #1013 for details.

Fixes #762.

source

@@ -2166,6 +2166,12 @@ a.setAttribute('href', 'http://example.com/'); // change the content attribute d
   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</span>.</p>
 
+  <p>A <dfn>node is 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>in a shadow-including
+  document</span>. Analogously, a <dfn>node is 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>in a shadow-including document</span>.</p>
+
 
   <h4>Scripting</h4>
 
@@ -58554,23 +58560,21 @@ o............A....e
   <hr>
 
   <p>When a <code>script</code> element that is not marked as being <span>"parser-inserted"</span>
-  experiences one of the events listed in the following list, the user agent must <span>immediately</span>
-  <span data-x="prepare a script">prepare</span> the <code>script</code> element:</p>
+  experiences one of the events listed in the following list, the user agent must
+  <span>immediately</span> <span data-x="prepare a script">prepare</span> the <code>script</code>
+  element:</p>
 
   <ul>
 
-   <li>The <code>script</code> element gets <span data-x="node is inserted into a document">inserted
-   into a document</span>, at the time the <span data-x="nodes are inserted">node is inserted</span>
-   according to the DOM, after any other <code>script</code> elements inserted at the same time that
-   are earlier in the <code>Document</code> in <span>tree order</span>.</li>
+   <li>The <code>script</code> element gets <span data-x="node is connected">connected</span>.</li>
 
-   <li>The <code>script</code> element is <span>in a <code>Document</code></span> and a node or
+   <li>The <code>script</code> element is <span>in a shadow-including document</span> and a node or
    document fragment is <span data-x="nodes are inserted">inserted</span> into the
    <code>script</code> element, after any <code>script</code> elements <span data-x="nodes are
    inserted">inserted</span> at that time.</li>
 
-   <li>The <code>script</code> element is <span>in a <code>Document</code></span> and has a <code
-   data-x="attr-script-src">src</code> attribute set where previously the element had no such
+   <li>The <code>script</code> element is <span>in a shadow-including document</span> and has a
+   <code data-x="attr-script-src">src</code> attribute set where previously the element had no such
    attribute.</li>
 
   </ul>
@@ -59118,9 +59122,9 @@ o............A....e
    <li>
 
     <p>If <span data-x="concept-script-type">the script's type</span> is "<code
-    data-x="">classic</code>", <span>fire a simple event</span> named <code
-    data-x="event-beforescriptexecute">beforescriptexecute</code> that bubbles and is cancelable
-    at the <code>script</code> element.</p>
+    data-x="">classic</code>" and the element is <span>in a document</span>, then <span>fire a
+    simple event</span> named <code data-x="event-beforescriptexecute">beforescriptexecute</code>
+    that bubbles and is cancelable at the <code>script</code> element.</p>
 
     <p>If the event is canceled, then abort these steps.</p>
 
@@ -59155,7 +59159,8 @@ o............A....e
       <ol>
        <li><p>Set the <code>script</code> element's <span>node document</span>'s <code
        data-x="dom-document-currentScript">currentScript</code> attribute to the
-       <code>script</code> element.</p></li>
+       <code>script</code> element, if the <code>script</code> element is <span>in a
+       document</span>, and to null otherwise.</p></li>
 
        <li><p><span data-x="run a classic script">Run the classic script</span> given by <span
        data-x="concept-script-script">the script's script</span>.</p></li>
@@ -59193,9 +59198,9 @@ o............A....e
    <li>
 
     <p>If <span data-x="concept-script-type">the script's type</span> is "<code
-    data-x="">classic</code>", <span>fire a simple event</span> named <code
-    data-x="event-afterscriptexecute">afterscriptexecute</code> that bubbles (but is not
-    cancelable) at the <code>script</code> element.</p>
+    data-x="">classic</code>" and the element is <span>in a document</span>, then <span>fire a
+    simple event</span> named <code data-x="event-afterscriptexecute">afterscriptexecute</code> that
+    bubbles (but is not cancelable) at the <code>script</code> element.</p>
 
    </li>
 
@@ -59208,6 +59213,7 @@ o............A....e
 
     <p>Otherwise <span>queue a task</span> to <span>fire a simple event</span> named <code
     data-x="event-load">load</code> at the <code>script</code> element.</p>
+    <!-- Shadow TODO: this event needs to be scoped -->
 
    </li>