Automatically fire AX events on Mac based on tree changes

ui/accessibility/ax_tree.cc

Index: ui/accessibility/ax_tree.cc
diff --git a/ui/accessibility/ax_tree.cc b/ui/accessibility/ax_tree.cc
index b2c0833204d2c7a415cda0442a467b8406b3a531..03b6aeb8a2cd5912f8e969bb1b9696e9004e27f6 100644
--- a/ui/accessibility/ax_tree.cc
+++ b/ui/accessibility/ax_tree.cc
@@ -154,10 +154,14 @@ AXNode* AXTree::GetFromId(int32_t id) const {
   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) {