ChromeVox should not speak live regions that aren't in the document.

The underlying issue is that by the time we get around to processing a live
region node from a mutation observer, the node may no longer be part of
the DOM, in which case we should treat it as invisible.

To fix it, fix cvox.DomUtil.hasInvisibleAncestor_ so that it returns
true (invisible) if passed an element that's not actually part of the
document.

BUG=408821

Review URL: https://codereview.chromium.org/517853002

Cr-Commit-Position: refs/heads/master@{#292847}

chrome/browser/resources/chromeos/chromevox/common/dom_util.js

@@ -193,7 +193,8 @@ cvox.DomUtil.computeIsVisible_ = function(
 /**
  * Checks the ancestor chain for the given node for invisibility. If an
  * ancestor is invisible and this cannot be overriden by a descendant,
- * we return true.
+ * we return true. If the element is not a descendant of the document
+ * element it will return true (invisible).
  * @param {Node} node The node to check the ancestor chain for.
  * @return {boolean} True if a descendant is invisible.
  * @private
@@ -205,8 +206,15 @@ cvox.DomUtil.hasInvisibleAncestor_ = function(node) {
     if (cvox.DomUtil.isInvisibleStyle(style, true)) {
       return true;
     }
+    // Once we reach the document element and we haven't found anything
+    // invisible yet, we're done. If we exit the while loop and never found
+    // the document element, the element wasn't part of the DOM and thus it's
+    // invisible.
+    if (ancestor == document.documentElement) {
+      return false;
+    }
   }
-  return false;
+  return true;
 };
 
 

chrome/browser/resources/chromeos/chromevox/common/dom_util_test.js

@@ -141,6 +141,12 @@ TEST_F('CvoxDomUtilUnitTest', 'IsVisible', function() {
   node = $('nested_visibility_hide');
   assertEquals(false,
       cvox.DomUtil.isVisible(node, {checkDescendants: false}));
+
+  // Test that an element not part of the DOM is treated as invisible.
+  var div = document.createElement('div');
+  assertEquals(false, cvox.DomUtil.isVisible(div));
+  document.body.appendChild(div);
+  assertEquals(true, cvox.DomUtil.isVisible(div));
 });
 
 /** Test determining if a node is a leaf node or not. @export */