Avoid sending desktop automation events on nodes that aren't in the tree.

It's not uncommon to get an event fired on a View whose ancestor Window
is invisible, so it's not actually in a reachable part of the
accessibility tree. Suppress sending events in those cases (but still
serialize tree changes to be safe).

This eliminates a lot of harmless but annoying warnings from
automation_node.js like
"Got locationChanged event on unknown node: 10; this: 311"

Bug: none
Change-Id: I4cc127f74d57953c9a4f6b5ecd44902a368730ca
Reviewed-on: https://chromium-review.googlesource.com/1225950
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592995}

chrome/browser/ui/aura/accessibility/automation_manager_aura.cc

@@ -250,10 +250,17 @@ void AutomationManagerAura::SendEvent(BrowserContext* context,
     event_bundle.updates.push_back(focused_node_update);
   }
 
-  ui::AXEvent event;
-  event.id = aura_obj->GetUniqueId().Get();
-  event.event_type = event_type;
-  event_bundle.events.push_back(event);
+  // Fire the event on the node, but only if it's actually in the tree.
+  // Sometimes we get events fired on nodes with an ancestor that's
+  // marked invisible, for example. In those cases we should still
+  // call SerializeChanges (because the change may have affected the
+  // ancestor) but we shouldn't fire the event on the node not in the tree.
+  if (current_tree_serializer_->IsInClientTree(aura_obj)) {
+    ui::AXEvent event;
+    event.id = aura_obj->GetUniqueId().Get();
+    event.event_type = event_type;
+    event_bundle.events.push_back(event);
+  }
 
   AutomationEventRouter* router = AutomationEventRouter::GetInstance();
   router->DispatchAccessibilityEvents(event_bundle);

ui/accessibility/ax_tree_serializer.h

@@ -88,6 +88,16 @@ class AXTreeSerializer {
   // being serialized.
   void InvalidateSubtree(AXSourceNode node);
 
+  // Return whether or not this node is in the client tree. If you call
+  // this immediately after serializing, this indicates whether a given
+  // node is in the set of nodes that the client (the recipient of
+  // the AXTreeUpdates) is aware of.
+  //
+  // For example, you could use this to determine if a given node is
+  // reachable. If one of its ancestors is hidden and it was pruned
+  // from the accessibility tree, this would return false.
+  bool IsInClientTree(AXSourceNode node);
+
   // Only for unit testing. Normally this class relies on getting a call
   // to SerializeChanges() every time the source tree changes. For unit
   // testing, it's convenient to create a static AXTree for the initial
@@ -432,6 +442,12 @@ void AXTreeSerializer<AXSourceNode, AXNodeData, AXTreeData>::InvalidateSubtree(
     InvalidateClientSubtree(client_node);
 }
 
+template <typename AXSourceNode, typename AXNodeData, typename AXTreeData>
+bool AXTreeSerializer<AXSourceNode, AXNodeData, AXTreeData>::IsInClientTree(
+    AXSourceNode node) {
+  return !!ClientTreeNodeById(tree_->GetId(node));
+}
+
 template <typename AXSourceNode, typename AXNodeData, typename AXTreeData>
 void AXTreeSerializer<AXSourceNode, AXNodeData, AXTreeData>::
     InvalidateClientSubtree(ClientTreeNode* client_node) {