Generate contextualized braille for horizontal trees

Bug: 819848
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: If57780e21ca7a865bb6d0318d3809db916c7db28
Reviewed-on: https://chromium-review.googlesource.com/969705Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544376}

chrome/browser/resources/chromeos/chromevox/cvox2/background/automation_predicate.js

@@ -532,8 +532,9 @@ AutomationPredicate.supportsImageData =
  * @return {boolean}
  */
 AutomationPredicate.contextualBraille = function(node) {
-  return node.parent != null && node.parent.role == Role.ROW &&
-      AutomationPredicate.cellLike(node);
+  return node.parent != null &&
+      ((node.parent.role == Role.ROW && AutomationPredicate.cellLike(node)) ||
+       (node.parent.role == Role.TREE && node.parent.state[State.HORIZONTAL]));
 };
 
 /**