Update checked predicate and trigger for hint

Bug: 876944
Change-Id: Iffe0ef328e018ee2f8ca6e36fab757caa3aad1d2
Reviewed-on: https://chromium-review.googlesource.com/1232255Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593770}

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

@@ -455,10 +455,9 @@ AutomationPredicate.shouldIgnoreNode = function(node) {
  * @param {!AutomationNode} node
  * @return {boolean}
  */
-AutomationPredicate.checkable = AutomationPredicate.roles([
-  Role.CHECK_BOX, Role.RADIO_BUTTON, Role.MENU_ITEM_CHECK_BOX,
-  Role.MENU_ITEM_RADIO, Role.SWITCH, Role.TOGGLE_BUTTON, Role.TREE_ITEM
-]);
+AutomationPredicate.checkable = function(node) {
+  return !!node.checked;
+};
 
 /**
  * Returns if the node is clickable.