Issue/1625 implement element closest

src/jsdom-patches.js

@@ -149,6 +149,21 @@ Node.prototype.insertBefore = function( /* Node */ newChild, /* Node*/ refChild
  */
 Element.prototype.matches = Element.prototype.matchesSelector;
 
+/*
+ * Implementation of Element.prototype.closest that it's missing from the jsdom-jscore fork we're using.
+ * See https://github.com/wordpress-mobile/gutenberg-mobile/issues/1625
+ */
+Element.prototype.closest = function( selector ) {
+	let el = this;
+	while ( el ) {
+		if ( el.matches( selector ) ) {
+			return el;
+		}
+		el = el.parentElement;
+	}
+	return null;
+};
+
 /**
  * Helper function to check if a node implements the NonDocumentTypeChildNode
  * interface