Move some AX attrs from AXNodeData to AXTreeData.

ui/accessibility/ax_tree_update.h

Index: ui/accessibility/ax_tree_update.h
diff --git a/ui/accessibility/ax_tree_update.h b/ui/accessibility/ax_tree_update.h
index 7fd94ec498ee9077ffbfdc181518cec51540c23b..c7d272fe10f2495f1df41ee89fad3bd32014929f 100644
--- a/ui/accessibility/ax_tree_update.h
+++ b/ui/accessibility/ax_tree_update.h
@@ -10,6 +10,7 @@
 
 #include "base/strings/string_number_conversions.h"
 #include "ui/accessibility/ax_node_data.h"
+#include "ui/accessibility/ax_tree_data.h"
 
 namespace ui {
 
@@ -21,8 +22,9 @@ namespace ui {
 //
 // An AXTreeUpdate consists of an optional node id to clear (meaning
 // that all of that node's children and their descendants are deleted),
-// followed by an ordered vector of AXNodeData structures to be applied
-// to the tree in order.
+// followed by an ordered vector of zero or more AXNodeData structures to
+// be applied to the tree in order. An update may also include an optional
+// update to the AXTreeData structure that applies to the tree as a whole.
 //
 // Suppose that the next AXNodeData to be applied is |node|. The following
 // invariants must hold:
@@ -38,9 +40,14 @@ namespace ui {
 //        placeholder must be updated within the same AXTreeUpdate, otherwise
 //        it's a fatal error. This guarantees the tree is always complete
 //        before or after an AXTreeUpdate.
-template<typename AXNodeData> struct AXTreeUpdate {
-  AXTreeUpdate();
-  ~AXTreeUpdate();
+template<typename AXNodeData, typename AXTreeData> struct AXTreeUpdateBase {
+  AXTreeUpdateBase();
+  ~AXTreeUpdateBase();
+
+  // If |has_tree_data| is true, the value of |tree_data| should be used
+  // to update the tree data, otherwise it should be ignored.
+  bool has_tree_data;
+  AXTreeData tree_data;
 
   // The id of a node to clear, before applying any updates,
   // or 0 if no nodes should be cleared. Clearing a node means deleting
@@ -58,17 +65,26 @@ template<typename AXNodeData> struct AXTreeUpdate {
   // TODO(dmazzoni): location changes
 };
 
-template<typename AXNodeData>
-AXTreeUpdate<AXNodeData>::AXTreeUpdate() : node_id_to_clear(0) {
+typedef AXTreeUpdateBase<AXNodeData, AXTreeData> AXTreeUpdate;
+
+template<typename AXNodeData, typename AXTreeData>
+AXTreeUpdateBase<AXNodeData, AXTreeData>::AXTreeUpdateBase()
+    : has_tree_data(false),
+      node_id_to_clear(0) {
 }
 
-template<typename AXNodeData>
-AXTreeUpdate<AXNodeData>::~AXTreeUpdate() {
+template<typename AXNodeData, typename AXTreeData>
+AXTreeUpdateBase<AXNodeData, AXTreeData>::~AXTreeUpdateBase() {
 }
 
-template<typename AXNodeData>
-std::string AXTreeUpdate<AXNodeData>::ToString() const {
+template<typename AXNodeData, typename AXTreeData>
+std::string AXTreeUpdateBase<AXNodeData, AXTreeData>::ToString() const {
   std::string result;
+
+  if (has_tree_data) {
+    result += "AXTreeUpdate tree data:" + tree_data.ToString();
+  }
+
   if (node_id_to_clear != 0) {
     result += "AXTreeUpdate: clear node " +
         base::IntToString(node_id_to_clear) + "\n";