Filter out output for unknown nodes

During touch exploration, we often hit test to unknown nodes.

Change-Id: I1f627c59045500c98ad5a63f1524a91d66ad2357
Reviewed-on: https://chromium-review.googlesource.com/1162701
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580979}

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

@@ -248,6 +248,14 @@ DesktopAutomationHandler.prototype = {
                    target, Dir.FORWARD, AutomationPredicate.object) ||
           target;
     }
+
+    while (target && !AutomationPredicate.object(target))
+      target = target.parent;
+
+
+    if (!target)
+      return;
+
     if (ChromeVoxState.instance.currentRange &&
         target == ChromeVoxState.instance.currentRange.start.node)
       return;

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

@@ -573,6 +573,7 @@ Output.RULES = {
           @describe_index($posInSet, $setSize)
           @describe_depth($hierarchicalLevel)`
     },
+    unknown: {speak: ``},
     window: {
       enter: `@describe_window($name)`,
       speak: `@describe_window($name) $earcon(OBJECT_OPEN)`
@@ -1766,10 +1767,16 @@ Output.prototype = {
     var parentRole = (Output.ROLE_INFO_[node.role] || {}).inherits;
     var parentRoleBlock = eventBlock[parentRole || ''] || {};
 
-    var format =
-        roleBlock.speak || parentRoleBlock.speak || eventBlock['default'].speak;
-    if (this.formatOptions_.braille)
-      format = roleBlock.braille || parentRoleBlock.braille || format;
+    var format = roleBlock.speak !== undefined ?
+        roleBlock.speak :
+        parentRoleBlock.speak !== undefined ? parentRoleBlock.speak :
+                                              eventBlock['default'].speak;
+    if (this.formatOptions_.braille) {
+      format = roleBlock.braille !== undefined ?
+          roleBlock.braille :
+          parentRoleBlock.braille !== undefined ? parentRoleBlock.braille :
+                                                  format;
+    }
 
     this.format_(node, format, buff, prevNode);