Add initStorageEvent()

Tests: web-platform-tests/wpt#13368

Fixes whatwg#1054.

source

@@ -94048,7 +94048,7 @@ typedef (<span>WindowProxy</span> or <span>MessagePort</span> or <span>ServiceWo
   value it was initialized to. It represents, in <span>cross-document messaging</span> and
   <span>channel messaging</span>, the <code>MessagePort</code> array being sent.</p>
 
-  <!-- handwave this one since it's deprecated anyway... let me know if there's interop issues -->
+  <!-- handwavy, file bugs if there are interop issues -->
   <p>The <dfn><code data-x="dom-MessageEvent-initMessageEvent">initMessageEvent()</code></dfn>
   method must initialize the event in a manner analogous to the similarly-named <code
   data-x="dom-Event-initEvent">initEvent()</code> method. <ref spec=DOM></p>
@@ -99216,6 +99216,8 @@ interface <dfn>StorageEvent</dfn> : <span>Event</span> {
   readonly attribute DOMString? <span data-x="dom-StorageEvent-newValue">newValue</span>;
   readonly attribute USVString <span data-x="dom-StorageEvent-url">url</span>;
   readonly attribute <span>Storage</span>? <span data-x="dom-StorageEvent-storageArea">storageArea</span>;
+
+  void <span data-x="dom-StorageEvent-initStorageEvent">initStorageEvent</span>(DOMString type, optional boolean bubbles = false, optional boolean cancelable = false, optional DOMString? key = null, optional DOMString? oldValue = null, optional DOMString? newValue = null, optional USVString url = "", optional Storage? storageArea = null);
 };
 
 dictionary <dfn>StorageEventInit</dfn> : <span>EventInit</span> {
@@ -99269,6 +99271,11 @@ dictionary <dfn>StorageEventInit</dfn> : <span>EventInit</span> {
   data-x="dom-StorageEvent-storageArea">storageArea</code></dfn> attributes must return the values
   they were initialized to.</p>
 
+  <!-- handwavy, file bugs if there are interop issues -->
+  <p>The <dfn><code data-x="dom-StorageEvent-initStorageEvent">initStorageEvent()</code></dfn>
+  method must initialize the event in a manner analogous to the similarly-named <code
+  data-x="dom-Event-initEvent">initEvent()</code> method. <ref spec=DOM></p>
+
   </div>