First step to move common accessibility code out of content.

ui/accessibility/ax_tree.h

+// Copyright (c) 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.
+
+#ifndef UI_ACCESSIBILITY_AX_TREE_H_
+#define UI_ACCESSIBILITY_AX_TREE_H_
+
+#include "base/containers/hash_tables.h"
+
+#include "ui/accessibility/ax_tree.h"
+#include "ui/accessibility/ax_tree_source.h"
+#include "ui/accessibility/ax_tree_update.h"
+#include "ui/base/ui_export.h"
+
+namespace ui {
+
+class AXNode;
+
+// AXTree is a live, managed tree of AXNode objects that can receive
+// updates from another AXTreeSource via AXTreeUpdates, and it can be
+// used as a source for sending updates to another client tree.
+// It's designed to be subclassed to ement support for native

[David Tseng, 2013/11/15 18:05:31]

Optional: I still think this design isn't a good abstraction for all of our use
cases. Namely, in the extension process, we don't need any of the facilities
provided by AXTreeSource.

Proposed alternative:
AXTreeSource stays as is.
Create a new interface called AXTreeReceiver which implements an
Unserialize(AXTreeUpdate) method along with anything else needed.

Thus,
Blink: only needs to implement the AXTreeSource interface.
Browser: needs to implement both AXTreeSource and AXTreeReceiver interfaces.
Extension: only needs to implement the AXTreeReceiver interface.

[David Tseng, 2013/11/15 18:05:31]

s/ement/implement

[dmazzoni, 2013/11/18 08:09:25]

Done.

[dmazzoni, 2013/11/18 08:09:25]

OK, I moved that part into a subclass, AXSerializableTree.

Right now I can't think of a time when we'd want an AXTree that's not a
receiver tree, so rather than split, let's leave it combined and refactor later
when needed. I don't want to add complexity to the class hierarchy that
we won't actually use.

+// accessibility APIs on a specific platform.
+class UI_EXPORT AXTree {
+ public:
+  AXTree();
+  explicit AXTree(const AXTreeUpdate& initial_state);
+  virtual ~AXTree();
+
+  virtual AXNode* GetRoot() const;
+  virtual AXNode* GetFromId(int32 id) const;
+  virtual bool Unserialize(const AXTreeUpdate& update);
+
+  // Get a TreeSource interface for this tree. The client gets ownership
+  // of the return value and should delete it when done.
+  virtual AXTreeSource<AXNode>* CreateTreeSource();

[David Tseng, 2013/11/15 18:05:31]

I think this method belongs on the AXTreeSource interface.

[dmazzoni, 2013/11/18 08:09:25]

This is now in AXSerializableTree.

+
+ protected:
+  // Subclasses can override this to use a subclass of AXNode.
+  virtual AXNode* CreateNode();
+
+  // This is called from within Unserialize(), it returns true on success.
+  // Subclasses can override this to do additional processing.
+  virtual bool UpdateNode(const AXNodeData& src);
+
+  // Subclasses can override this to do special behavior when the root changes.
+  virtual void OnRootChanged();
+
+ private:
+  // Convenience function to create a node and call Initialize on it.
+  AXNode* CreateAndInitializeNode(
+      AXNode* parent, int32 id, int32 index_in_parent);
+
+  // Call Destroy() on |node|, and delete it from the id map, and then
+  // call recursively on all nodes in its subtree.
+  void DestroyNodeAndSubtree(AXNode* node);
+
+  // Iterate over the children of |node| and for each child, destroy the
+  // child and its subtree if its id is not in |new_child_ids|. Returns
+  // true on success, false on fatal error.
+  bool DeleteOldChildren(AXNode* node,
+                         const std::vector<int32> new_child_ids);
+
+  // Iterate over |new_child_ids| and populate |new_children| with
+  // pointers to child nodes, reusing existing nodes already in the tree
+  // if they exist, and creating otherwise. Reparenting is disallowed, so
+  // if the id already exists as the child of another node, that's an
+  // error. Returns true on success, false on fatal error.
+  bool CreateNewChildVector(AXNode* node,
+                            const std::vector<int32> new_child_ids,
+                            std::vector<AXNode*>* new_children);
+
+  AXNode* root_;
+  base::hash_map<int32, AXNode*> id_map_;
+};
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_AX_TREE_H_