Examples: Added ids to ARButtom and VRButton.

examples/jsm/webxr/ARButton.js

@@ -120,6 +120,7 @@ var ARButton = {
 		if ( 'xr' in navigator ) {
 
 			var button = document.createElement( 'button' );
+			button.id = 'ARButton';
 			button.style.display = 'none';
 
 			stylizeElement( button );

examples/jsm/webxr/VRButton.js

@@ -127,6 +127,7 @@ var VRButton = {
 		if ( 'xr' in navigator ) {
 
 			var button = document.createElement( 'button' );
+			button.id = 'VRButton';
 			button.style.display = 'none';
 
 			stylizeElement( button );