fix(dialog): thread blocking during large DOM traversals (#10552) (#11193)

Author: Splaktar

src/components/dialog/dialog.js

@@ -536,7 +536,7 @@ function MdDialogDirective($$rAF, $mdTheming, $mdDialog) {
  *     `three` into the controller, with the value 3. If `bindToController` is true, they will be
  *     copied to the controller instead.
  *   - `bindToController` - `bool`: bind the locals to the controller, instead of passing them in.
- *   - `resolve` - `{function=}`: Similar to locals, except it takes as values functions that return promises, and the	
+ *   - `resolve` - `{function=}`: Similar to locals, except it takes as values functions that return promises, and the
  *      dialog will not open until all of the promises resolve.
  *   - `controllerAs` - `{string=}`: An alias to assign the controller to on the scope.
  *   - `parent` - `{element=}`: The element to append the dialog to. Defaults to appending
@@ -1145,35 +1145,46 @@ function MdDialogProvider($$interimElementProvider) {
       // get raw DOM node
       walkDOM(element[0]);
 
-      options.unlockScreenReader = function() {
+      options.unlockScreenReader = function () {
         isHidden = false;
         walkDOM(element[0]);
 
         options.unlockScreenReader = null;
       };
 
       /**
-       * Walk DOM to apply or remove aria-hidden on sibling nodes
-       * and parent sibling nodes
-       *
+       * Get all of an element's parent elements up the DOM tree
+       * @return {Array} The parent elements
        */
-      function walkDOM(element) {
+      function getParents(element) {
+        var parents = [];
         while (element.parentNode) {
           if (element === document.body) {
-            return;
+            return parents;
           }
           var children = element.parentNode.children;
           for (var i = 0; i < children.length; i++) {
             // skip over child if it is an ascendant of the dialog
-            // or a script or style tag
+            // a script or style tag, or a live region.
             if (element !== children[i] &&
-             !isNodeOneOf(children[i], ['SCRIPT', 'STYLE']) &&
-             !children[i].hasAttribute('aria-live')) {
-              children[i].setAttribute('aria-hidden', isHidden);
+                !isNodeOneOf(children[i], ['SCRIPT', 'STYLE']) &&
+                !children[i].hasAttribute('aria-live')) {
+              parents.push(children[i]);
             }
           }
+          element = element.parentNode;
+        }
+        return parents;
+      }
 
-          walkDOM(element = element.parentNode);
+      /**
+       * Walk DOM to apply or remove aria-hidden on sibling nodes
+       * and parent sibling nodes
+       */
+      function walkDOM(element) {
+        var elements = getParents(element);
+        for (var i = 0; i < elements.length; i++) {
+          elements[i].setAttribute('aria-hidden', isHidden);
         }
       }
     }