Shadow: add "retargeting steps" to the dispatch algorithm

Add a "retargeting steps" hook to the dispatch algorithm so other specifications can adjust an event's internal slots before the event listeners of event's path are invoked.

This hook will be used in Touch Events. Fixes #286.

dom.bs

@@ -651,6 +651,11 @@ list of tuples, each of which consists of an <b>item</b> (an {{EventTarget}} obj
 object). A tuple is formatted as (<b>item</b>, <b>target</b>, <b>relatedTarget</b>). A <a
 for=Event>path</a> is initially the empty list.</p>
 
+<p><a lt="Other applicable specifications">Specifications</a> may define
+<dfn export for=Event>retargeting steps</dfn> for all or some <a>events</a>.
+The algorithm is passed <var>event</var>, as indicated in the <a>dispatch</a>
+algorithm below.
+
 <dl class=domintro>
  <dt><code><var>event</var> = new <a constructor lt="Event()">Event</a>(<var>type</var> [, <var>eventInitDict</var>])</code>
  <dd>Returns a new <var>event</var> whose
@@ -1236,6 +1241,8 @@ for discussion).
 
    <li><p>Set <var>event</var>'s <a>relatedTarget</a> to <var>tuple</var>'s <b>relatedTarget</b>.
 
+   <li><p>Run the <a>retargeting steps</a> with <var>event</var>.
+
    <li><p>If <var>tuple</var>'s <b>target</b> is null, then <a>invoke</a> <var>tuple</var>'s
    <b>item</b> with <var>event</var>.
   </ol>
@@ -1250,6 +1257,8 @@ for discussion).
 
    <li><p>Set <var>event</var>'s <a>relatedTarget</a> to <var>tuple</var>'s <b>relatedTarget</b>.
 
+   <li><p>Run the <a>retargeting steps</a> with <var>event</var>.
+
    <li><p>If <var>tuple</var>'s <b>target</b> is non-null, then set <var>event</var>'s
    {{Event/eventPhase}} attribute to {{Event/AT_TARGET}}.
 

dom.html

@@ -71,7 +71,7 @@
    <p data-fill-with="logo"><a class="logo" href="https://whatwg.org/"> <img alt="WHATWG" height="100" src="https://resources.whatwg.org/logo-dom.svg"> </a> </p>
    <hgroup>
     <h1 class="p-name no-ref allcaps" id="title">DOM</h1>
-    <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2016-07-22">22 July 2016</time></span></h2>
+    <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2016-08-04">4 August 2016</time></span></h2>
    </hgroup>
    <div data-fill-with="spec-metadata">
     <dl>
@@ -525,6 +525,8 @@ <h3 class="heading settled" data-level="3.2" id="interface-event"><span class="s
    <p class="note" role="note">Other specifications use <a data-link-type="dfn" href="#event-relatedtarget">relatedTarget</a> to define a <code>relatedTarget</code> attribute. <a data-link-type="biblio" href="#biblio-uievents">[UIEVENTS]</a> </p>
    <p>An <a data-link-type="dfn" href="#concept-event">event</a> has an associated <dfn data-dfn-for="Event" data-dfn-type="dfn" data-export="" id="event-path">path<a class="self-link" href="#event-path"></a></dfn>. A <a data-link-type="dfn" href="#event-path">path</a> is a
 list of tuples, each of which consists of an <b>item</b> (an <code class="idl"><a data-link-type="idl" href="#eventtarget">EventTarget</a></code> object), <b>target</b> (null or an <code class="idl"><a data-link-type="idl" href="#eventtarget">EventTarget</a></code> object), and a <b>relatedTarget</b> (null or an <code class="idl"><a data-link-type="idl" href="#eventtarget">EventTarget</a></code> object). A tuple is formatted as (<b>item</b>, <b>target</b>, <b>relatedTarget</b>). A <a data-link-type="dfn" href="#event-path">path</a> is initially the empty list.</p>
+   <p><a data-link-type="dfn" href="#other-applicable-specifications">Specifications</a> may define <dfn data-dfn-for="Event" data-dfn-type="dfn" data-export="" id="event-retargeting-steps">retargeting steps<a class="self-link" href="#event-retargeting-steps"></a></dfn> for all or some <a data-link-type="dfn" href="#concept-event">events</a>.
+The algorithm is passed <var>event</var>, as indicated in the <a data-link-type="dfn" href="#concept-event-dispatch">dispatch</a> algorithm below. </p>
    <dl class="domintro">
     <dt><code><var>event</var> = new <a class="idl-code" data-link-type="constructor" href="#dom-event-event">Event</a>(<var>type</var> [, <var>eventInitDict</var>])</code> 
     <dd>Returns a new <var>event</var> whose <code class="idl"><a data-link-type="idl" href="#dom-event-type">type</a></code> attribute value is set to <var>type</var>. The optional <var>eventInitDict</var> argument
@@ -903,6 +905,8 @@ <h3 class="heading settled" data-level="3.8" id="dispatching-events"><span class
    in <var>event</var>’s <a data-link-type="dfn" href="#event-path">path</a>, that is either <var>tuple</var> or preceding <var>tuple</var>, whose <b>target</b> is non-null. </p>
       <li>
        <p>Set <var>event</var>’s <a data-link-type="dfn" href="#event-relatedtarget">relatedTarget</a> to <var>tuple</var>’s <b>relatedTarget</b>. </p>
+      <li>
+       <p>Run the <a data-link-type="dfn" href="#event-retargeting-steps">retargeting steps</a> with <var>event</var>. </p>
       <li>
        <p>If <var>tuple</var>’s <b>target</b> is null, then <a data-link-type="dfn" href="#concept-event-listener-invoke">invoke</a> <var>tuple</var>’s <b>item</b> with <var>event</var>. </p>
      </ol>
@@ -914,6 +918,8 @@ <h3 class="heading settled" data-level="3.8" id="dispatching-events"><span class
    in <var>event</var>’s <a data-link-type="dfn" href="#event-path">path</a>, that is either <var>tuple</var> or preceding <var>tuple</var>, whose <b>target</b> is non-null. </p>
       <li>
        <p>Set <var>event</var>’s <a data-link-type="dfn" href="#event-relatedtarget">relatedTarget</a> to <var>tuple</var>’s <b>relatedTarget</b>. </p>
+      <li>
+       <p>Run the <a data-link-type="dfn" href="#event-retargeting-steps">retargeting steps</a> with <var>event</var>. </p>
       <li>
        <p>If <var>tuple</var>’s <b>target</b> is non-null, then set <var>event</var>’s <code class="idl"><a data-link-type="idl" href="#dom-event-eventphase">eventPhase</a></code> attribute to <code class="idl"><a data-link-type="idl" href="#dom-event-at_target">AT_TARGET</a></code>. </p>
       <li>
@@ -6116,6 +6122,7 @@ <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="c
    <li><a href="#represented-by-the-collection">represented by the collection</a><span>, in §4.2.10</span>
    <li><a href="#retarget">retarget</a><span>, in §4.8</span>
    <li><a href="#retarget">retargeting</a><span>, in §4.8</span>
+   <li><a href="#event-retargeting-steps">retargeting steps</a><span>, in §3.2</span>
    <li>
     root
     <ul>