First step to move common accessibility code out of content.

content/common/ax_tree_source.h

Index: content/common/ax_tree_source.h
diff --git a/content/common/ax_tree_source.h b/content/common/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 CONTENT_COMMON_AX_TREE_SOURCE_H_
+#define CONTENT_COMMON_AX_TREE_SOURCE_H_
+
+#include "content/public/common/ax_node_data.h"
+
+namespace content {
+
+// 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 AXSourceNode>
+class CONTENT_EXPORT AXTreeSource {
+ public:
+  virtual AXSourceNode* GetRoot() const = 0;
+  virtual int32 GetRootId() const = 0;
+  virtual AXSourceNode* GetFromId(int32 id) const = 0;
+  virtual int32 GetId(const AXSourceNode* node) const = 0;
+  virtual int GetChildCount(const AXSourceNode* node) const = 0;
+  virtual AXSourceNode* GetChildAtIndex(const AXSourceNode* 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 AXSourceNode* node) const = 0;
+
+  virtual void Serialize(const AXSourceNode* node, AXNodeData* out_data) const
+      = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_AX_TREE_SOURCE_H_