[web-animations-1] Move definition of getAnimations from Document to DocumentOrShadowRoot (#3959)

This fixes #3951.

Author: birtles

web-animations-1/Overview.bs

@@ -192,6 +192,7 @@ urlPrefix: https://drafts.csswg.org/css-style-attr/; type: dfn; spec: css-style-
 <pre class="link-defaults">
 spec:dom; type:interface; text:EventTarget
 spec:dom; type:interface; text:Event
+spec:dom; type:dfn; for:/; text:shadow root
 spec:css-values-3; type:type; text:<ident>
 spec:css-backgrounds-3; type:property;
     text:border-width
@@ -5851,13 +5852,12 @@ animation.play();</pre>
 
 <h3 id="extensions-to-the-document-interface">Extensions to the <code>Document</code> interface</h3>
 
-The following extensions are made to the <a lt='Document' interface>Document
-interface</a> defined in [[!DOM]].
+The following extensions are made to the {{Document}} interface defined in
+[[!DOM]].
 
 <pre class="idl">
 partial interface Document {
     readonly attribute DocumentTimeline timeline;
-    sequence&lt;Animation&gt; getAnimations();
 };
 </pre>
 
@@ -5869,13 +5869,26 @@ partial interface Document {
 
 </div>
 
+<h3 id="extensions-to-the-documentorshadowroot-interface-mixin">Extensions to the <code>DocumentOrShadowRoot</code> interface mixin</h3>
+
+The following extensions are made to the {{DocumentOrShadowRoot}} interface
+mixin defined in [[!DOM]].
+
+<pre class="idl">
+partial interface mixin DocumentOrShadowRoot {
+    sequence&lt;Animation&gt; getAnimations();
+};
+</pre>
+
 <div class="methods">
 
-:   <dfn method for=Document lt='getAnimations()'>
+:   <dfn method for=DocumentOrShadowRoot lt='getAnimations()'>
     sequence&lt;Animation&gt; getAnimations()</dfn>
 ::  Returns the set of [=relevant=] {{Animation}} objects
     that have an associated <a>target effect</a>
-    whose <a>target element</a> is a <a>descendant</a> of the document.
+    whose <a>target element</a> is a <a>descendant</a> of
+    the [=document=] or [=shadow root=]
+    on which this method is called.
 
     The returned list is sorted using the composite order described
     for the associated <a>animations</a> of effects in [[#the-effect-stack]].
@@ -5887,6 +5900,7 @@ partial interface Document {
 
 </div>
 
+
 <h3 id="extensions-to-the-element-interface">Extensions to the <code>Element</code> interface</h3>
 
 Since DOM Elements may be the target of an animation,
@@ -5901,7 +5915,6 @@ This allows the following kind of usage.
 <div class="example"><pre class="lang-javascript">
 elem.animate({ color: 'red' }, 2000);</pre></div>
 
-
 <h3 id="extensions-to-the-pseudoelement-interface">Extensions to the <code>CSSPseudoElement</code> interface</h3>
 
 Since <a>keyframe effects</a> may also target pseudo-elements, the
@@ -6219,6 +6232,9 @@ The following changes have been made since the <a
 *   Added an {{Animatable/getAnimations(options)/options}} parameter to the
     {{Animatable/getAnimations()}} method on the {{Animatable}} interface
     to allow fetching all animations on descendants of a particular element.
+*   Moved the definition of {{DocumentOrShadowRoot/getAnimations()}} from the
+    {{Document}} interface to the {{DocumentOrShadowRoot}} interface mixin
+    so that it can be used with {{ShadowRoot}}s as well.
 
 The <a
   href="https://github.com/w3c/csswg-drafts/commits/master/web-animations-1">changelog</a>