First step to move common accessibility code out of content.

content/public/common/ax_tree.h

Index: content/public/common/ax_tree.h
diff --git a/content/public/common/ax_tree.h b/content/public/common/ax_tree.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_PUBLIC_COMMON_AX_TREE_H_
+#define CONTENT_PUBLIC_COMMON_AX_TREE_H_
+
+#include "content/common/content_export.h"
+#include "content/public/common/ax_node.h"
+#include "content/public/common/ax_tree_update.h"
+
+namespace content {
+
+// AXTree is a live, managed tree of AXNode objects that can receive
+// updates from another tree via AXTreeUpdates.
+class CONTENT_EXPORT AXTree {
+ public:
+  static AXTree* Create(const AXTreeUpdate& initial_state);
+
+  virtual AXNode* GetRoot() const = 0;
+  virtual AXNode* GetFromId(int32 id) const = 0;
+
+  // Apply an update from another tree.
+  virtual bool Unserialize(const AXTreeUpdate& update) = 0;
+
+ protected:
+  AXTree();
+  virtual ~AXTree();
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_COMMON_AX_TREE_H_