First step to move common accessibility code out of content.

ui/accessibility/ax_tree_source.h

Index: ui/accessibility/ax_tree_source.h
diff --git a/ui/accessibility/ax_tree_source.h b/ui/accessibility/ax_tree_source.h
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+// 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_SOURCE_H_
+#define UI_ACCESSIBILITY_AX_TREE_SOURCE_H_
+
+#include "ui/accessibility/ax_node_data.h"
+
+namespace ui {
+
+// An AXTreeSource is an abstract interface for a serializable
+// accessibility tree. The tree may be in some other format or
+// may be computed dynamically, but maintains the properties that
+// it's a strict tree, it has a unique id for each node, and all
+// of the accessibility information about a node can be serialized
+// as an AXNodeData. This is the primary interface to use when
+// an accessibility tree will be sent over an IPC before being
+// consumed.
+template<class AXNodeSource>
+class AX_EXPORT AXTreeSource {
+ public:
+  virtual ~AXTreeSource() {}
+  virtual AXNodeSource* GetFromId(int32 id) const = 0;
+  virtual int32 GetId(const AXNodeSource* node) const = 0;
+  virtual int GetChildCount(const AXNodeSource* node) const = 0;
+  virtual AXNodeSource* GetChildAtIndex(const AXNodeSource* node, int index)
+      const = 0;
+
+  // Returns the id of this node's parent, or 0 if it doesn't have a parent.
+  virtual int32 GetParentId(const AXNodeSource* node) const = 0;
+
+  // Serialize one node in the tree.
+  virtual void SerializeNode(
+      const AXNodeSource* node, AXNodeData* out_data) const = 0;
+
+ protected:
+  AXTreeSource() {}
+};
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_AX_TREE_SOURCE_H_