Automatically fire AX events on Mac based on tree changes

ui/accessibility/ax_tree.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/accessibility/ax_tree.h"
 
 #include <stddef.h>
 
 #include <set>
 
@@ skipping 136 matching lines @@
 
 void AXTree::SetDelegate(AXTreeDelegate* delegate) {
   delegate_ = delegate;
 }
 
 AXNode* AXTree::GetFromId(int32_t id) const {
   base::hash_map<int32_t, AXNode*>::const_iterator iter = id_map_.find(id);
   return iter != id_map_.end() ? iter->second : NULL;
 }
 
-void AXTree::UpdateData(const AXTreeData& data) {
-  data_ = data;
+void AXTree::UpdateData(const AXTreeData& new_data) {
+  if (data_ == new_data)
+    return;
+
+  AXTreeData old_data = data_;
+  data_ = new_data;
   if (delegate_)
-    delegate_->OnTreeDataChanged(this);
+    delegate_->OnTreeDataChanged(this, old_data, new_data);
 }
 
 bool AXTree::Unserialize(const AXTreeUpdate& update) {
   AXTreeUpdateState update_state;
   int32_t old_root_id = root_ ? root_->id() : 0;
 
   // First, make a note of any nodes we will touch as part of this update.
   for (size_t i = 0; i < update.nodes.size(); ++i)
     update_state.changed_node_ids.insert(update.nodes[i].id);
 
@@ skipping 322 matching lines @@
       update_state->pending_nodes.insert(child);
       update_state->new_nodes.insert(child);
     }
     new_children->push_back(child);
   }
 
   return success;
 }
 
 }  // namespace ui