First step to move common accessibility code out of content.

ui/accessibility/ax_tree_update.cc

Index: ui/accessibility/ax_tree_update.cc
diff --git a/ui/base/models/dialog_model.cc b/ui/accessibility/ax_tree_update.cc
similarity index 65%
copy from ui/base/models/dialog_model.cc
copy to ui/accessibility/ax_tree_update.cc
index 310bff04c5027dee495cf98b5f4512dda1a3fc46..3e80f0b1b7903cee751523a22385458e53865c66 100644
--- a/ui/base/models/dialog_model.cc
+++ b/ui/accessibility/ax_tree_update.cc
@@ -2,11 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ui/base/models/dialog_model.h"
+#include "ui/accessibility/ax_tree_update.h"
 
 namespace ui {
 
-DialogModel::~DialogModel() {
+AXTreeUpdate::AXTreeUpdate() {
+}
+
+AXTreeUpdate::~AXTreeUpdate() {
 }
 
 }  // namespace ui