Make tree serialization more robust and add more unit tests.

ui/accessibility/ax_tree.h

Index: ui/accessibility/ax_tree.h
diff --git a/ui/accessibility/ax_tree.h b/ui/accessibility/ax_tree.h
index 84108e05910d99572c0423e20579388b9d0691af..a56a0b2754130d48b4f624083d883aa2067f55c7 100644
--- a/ui/accessibility/ax_tree.h
+++ b/ui/accessibility/ax_tree.h
@@ -5,8 +5,9 @@
 #ifndef UI_ACCESSIBILITY_AX_TREE_H_
 #define UI_ACCESSIBILITY_AX_TREE_H_
 
-#include "base/containers/hash_tables.h"
+#include <set>
 
+#include "base/containers/hash_tables.h"
 #include "ui/accessibility/ax_export.h"
 #include "ui/accessibility/ax_tree.h"
 #include "ui/accessibility/ax_tree_update.h"
@@ -29,15 +30,23 @@ class AX_EXPORT AXTree {
   virtual AXNode* GetRoot() const;
   virtual AXNode* GetFromId(int32 id) const;
 
+  // Returns true on success. If it returns false, it's a fatal error
+  // and this tree should be destroyed, and the source of the tree update
+  // should not be trusted any longer.
   virtual bool Unserialize(const AXTreeUpdate& update);
 
+  // A string describing the error from an unsuccessful Unserialize,
+  // for testing and debugging.
+  const std::string& error() { return error_; }
+
  protected:
   // Subclasses can override this to use a subclass of AXNode.
   virtual AXNode* CreateNode(AXNode* parent, int32 id, int32 index_in_parent);
 
   // This is called from within Unserialize(), it returns true on success.
   // Subclasses can override this to do additional processing.

[aboxhall, 2013/12/02 17:18:08]

Could you comment what orphaned_nodes is used for?

[dmazzoni, 2013/12/03 08:35:04]

Done. Sorry, I renamed it to pending_nodes in the impl, so that's fixed too.

-  virtual bool UpdateNode(const AXNodeData& src);
+  virtual bool UpdateNode(const AXNodeData& src,
+                          std::set<AXNode*>* orphaned_nodes);
 
   // Subclasses can override this to do special behavior when the root changes.
   virtual void OnRootChanged();
@@ -64,10 +73,12 @@ class AX_EXPORT AXTree {
   // error. Returns true on success, false on fatal error.

[aboxhall, 2013/12/02 17:18:08]

Could you comment what pending_nodes is used for?

[dmazzoni, 2013/12/03 08:35:04]

Done.

   bool CreateNewChildVector(AXNode* node,
                             const std::vector<int32> new_child_ids,
-                            std::vector<AXNode*>* new_children);
+                            std::vector<AXNode*>* new_children,
+                            std::set<AXNode*>* pending_nodes);
 
   AXNode* root_;
   base::hash_map<int32, AXNode*> id_map_;
+  std::string error_;
 };
 
 }  // namespace ui