Original patch by rlarocque@chromium.org at http://codereview.chromium.org/7633077/

chrome/browser/sync/internal_api/read_node.h

Index: chrome/browser/sync/internal_api/read_node.h
diff --git a/chrome/browser/sync/internal_api/read_node.h b/chrome/browser/sync/internal_api/read_node.h
new file mode 100644
index 0000000000000000000000000000000000000000..9ad971501d473b09a6dd561ccfbde77349e24d12
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+++ b/chrome/browser/sync/internal_api/read_node.h
@@ -0,0 +1,79 @@
+// Copyright (c) 2011 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 CHROME_BROWSER_SYNC_INTERNAL_API_READ_NODE_H_
+#define CHROME_BROWSER_SYNC_INTERNAL_API_READ_NODE_H_
+#pragma once
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "chrome/browser/sync/internal_api/base_node.h"
+#include "chrome/browser/sync/syncable/model_type.h"
+
+namespace sync_pb {
+class AppSpecifics;
+class AutofillSpecifics;
+class AutofillProfileSpecifics;
+class BookmarkSpecifics;
+class EntitySpecifics;
+class ExtensionSpecifics;
+class SessionSpecifics;
+class NigoriSpecifics;
+class PreferenceSpecifics;
+class PasswordSpecificsData;
+class ThemeSpecifics;
+class TypedUrlSpecifics;
+}
+
+namespace sync_api {
+
+// ReadNode wraps a syncable::Entry to provide the functionality of a
+// read-only BaseNode.
+class ReadNode : public BaseNode {
+ public:
+  // Create an unpopulated ReadNode on the given transaction.  Call some flavor
+  // of Init to populate the ReadNode with a database entry.
+  explicit ReadNode(const BaseTransaction* transaction);
+  virtual ~ReadNode();
+
+  // A client must use one (and only one) of the following Init variants to
+  // populate the node.
+
+  // BaseNode implementation.
+  virtual bool InitByIdLookup(int64 id);
+  virtual bool InitByClientTagLookup(syncable::ModelType model_type,
+      const std::string& tag);
+
+  // There is always a root node, so this can't fail.  The root node is
+  // never mutable, so root lookup is only possible on a ReadNode.
+  void InitByRootLookup();
+
+  // Each server-created permanent node is tagged with a unique string.
+  // Look up the node with the particular tag.  If it does not exist,
+  // return false.
+  bool InitByTagLookup(const std::string& tag);
+
+  // Implementation of BaseNode's abstract virtual accessors.
+  virtual const syncable::Entry* GetEntry() const;
+  virtual const BaseTransaction* GetTransaction() const;
+
+ protected:
+  ReadNode();
+
+ private:
+  void* operator new(size_t size);  // Node is meant for stack use only.
+
+  // The underlying syncable object which this class wraps.
+  syncable::Entry* entry_;
+
+  // The sync API transaction that is the parent of this node.
+  const BaseTransaction* transaction_;
+
+  DISALLOW_COPY_AND_ASSIGN(ReadNode);
+};
+
+}  // namespace sync_api
+
+#endif  // CHROME_BROWSER_SYNC_INTERNAL_API_READ_NODE_H_