Make tree serialization more robust and add more unit tests.

ui/accessibility/ax_serializable_tree.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/accessibility/ax_serializable_tree.h"
 
 #include "ui/accessibility/ax_node.h"
 
 namespace ui {
 
 // This class is an implementation of the AXTreeSource interface with
 // AXNode as the node type, that just delegates to an AXTree. The purpose
 // of this is so that AXTreeSerializer only needs to work with the
 // AXTreeSource abstraction and doesn't need to actually know about
 // AXTree directly. Another AXTreeSource is used to abstract the Blink
 // accessibility tree.
 class AX_EXPORT AXTreeSourceAdapter : public AXTreeSource<AXNode> {
  public:
   AXTreeSourceAdapter(AXTree* tree) : tree_(tree) {}
   virtual ~AXTreeSourceAdapter() {}
 
   // AXTreeSource implementation.
+  virtual AXNode* GetRoot() const OVERRIDE {
+    return tree_->GetRoot();
+  }
+
   virtual AXNode* GetFromId(int32 id) const OVERRIDE {
     return tree_->GetFromId(id);
   }
 
   virtual int32 GetId(const AXNode* node) const OVERRIDE {
     return node->id();
   }
 
   virtual int GetChildCount(const AXNode* node) const OVERRIDE {
     return node->child_count();
   }
 
   virtual AXNode* GetChildAtIndex(const AXNode* node, int index)
       const OVERRIDE {
     return node->ChildAtIndex(index);
   }
 
-  virtual int32 GetParentId(const AXNode* node) const OVERRIDE {
-    if (node->parent())
-      return node->parent()->id();
-    else
-      return 0;
+  virtual AXNode* GetParent(const AXNode* node) const OVERRIDE {
+    return node->parent();
   }
 
   virtual void SerializeNode(
       const AXNode* node, AXNodeData* out_data) const OVERRIDE {
     *out_data = node->data();
   }
 
  private:
   AXTree* tree_;
 };
 
 AXSerializableTree::AXSerializableTree()
     : AXTree() {}
 
 AXSerializableTree::AXSerializableTree(const AXTreeUpdate& initial_state)
     : AXTree(initial_state) {
 }
 
 AXSerializableTree::~AXSerializableTree() {
 }
 
 AXTreeSource<AXNode>* AXSerializableTree::CreateTreeSource() {
   return new AXTreeSourceAdapter(this);
 }
 
 }  // namespace ui