Refactor content/renderer/accessibility to use AXTreeSerializer (re-land).

content/renderer/accessibility/renderer_accessibility_focus_only.cc

Index: content/renderer/accessibility/renderer_accessibility_focus_only.cc
diff --git a/content/renderer/accessibility/renderer_accessibility_focus_only.cc b/content/renderer/accessibility/renderer_accessibility_focus_only.cc
index 651b30b32b9e76452a4f0f0291b100d33f56f76a..cebba6f7a42d46656100ad3002ced51365f368f6 100644
--- a/content/renderer/accessibility/renderer_accessibility_focus_only.cc
+++ b/content/renderer/accessibility/renderer_accessibility_focus_only.cc
@@ -97,9 +97,9 @@ void RendererAccessibilityFocusOnly::HandleFocusedNodeChanged(
   // has focus, otherwise the focused node.
   event.id = node_has_focus ? next_id_ : 1;
 
-  event.nodes.resize(2);
-  ui::AXNodeData& root = event.nodes[0];
-  ui::AXNodeData& child = event.nodes[1];
+  event.update.nodes.resize(2);
+  ui::AXNodeData& root = event.update.nodes[0];
+  ui::AXNodeData& child = event.update.nodes[1];
 
   // Always include the root of the tree, the document. It always has id 1.
   root.id = 1;