Only allow one shadowRoot.

sky/engine/web/tests/data/touch-action-tests.js

 // Disable compositor hit testing
 document.addEventListener('touchstart', function() {});
 
 window.addEventListener('load', function() {
   // Create any shadow DOM nodes requested by the test.
   var shadowTrees = document.querySelectorAll('[make-shadow-dom]');
-  if (shadowTrees.length > 0 && !HTMLElement.prototype.createShadowRoot) {
+  if (shadowTrees.length > 0 && !HTMLElement.prototype.ensureShadowRoot) {
     document.body.innerHTML = 'ERROR: Shadow DOM not supported!';
     return;
   }
   for (var i = 0; i < shadowTrees.length; i++) {
     var tree = shadowTrees[i];
     var host = tree.previousElementSibling;
     if (!host.hasAttribute('shadow-host')) {
       document.body.innerHTML = 'ERROR: make-shadow-dom node must follow a shadow-host node';
       return;
     }
     tree.parentElement.removeChild(tree);
-    var shadowRoot = host.createShadowRoot();
+    var shadowRoot = host.ensureShadowRoot();
     shadowRoot.appendChild(tree);
   }
 });
 
 /*
  * Visualization of hit test locations for manual testing.
  * To be invoked manually (so it doesn't intefere with testing).
  */
 function addMarker(x, y)
 {
     const kMarkerSize = 6;
     var marker = document.createElement('div');
     marker.className = 'marker';
     marker.style.top = (y - kMarkerSize/2) + 'px';
     marker.style.left = (x - kMarkerSize/2) + 'px';
     document.body.appendChild(marker);
 }
 
 function addMarkers()
 {
   var tests = document.querySelectorAll('[expected-action]');
   for (var i = 0; i < tests.length; i++) {
     var r = tests[i].getClientRects()[0];
     addMarker(r.left, r.top);
     addMarker(r.right - 1, r.bottom - 1);
     addMarker(r.left + r.width / 2, r.top + r.height / 2);
   }
 }