Implement new SyncAPI and convert Preferences to it.

chrome/browser/sync/api/sync_change.h

+// 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_API_SYNC_CHANGE_H_
+#define CHROME_BROWSER_SYNC_API_SYNC_CHANGE_H_
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "chrome/browser/sync/api/sync_data.h"
+
+// A SyncChange object reflects a change to a piece of synced data. The change
+// can be either a delete, add, or an update. All data relevant to the change
+// is encapsulated within the SyncChange, which, once created, is immutable.
+// Note: it is safe and cheap to pass these by value or make copies, as they do
+// not create deep copies of their internal data.
+class SyncChange {
+ public:
+  enum SyncChangeType {
+    ACTION_INVALID,
+    ACTION_ADD,
+    ACTION_UPDATE,
+    ACTION_DELETE
+  };
+
+  // Default constructor creates an invalid change.
+  SyncChange();
+  // Create a new change with the specified sync data.
+  SyncChange(SyncChangeType change_type, const SyncData& sync_data);
+  ~SyncChange();
+
+  // Copy constructor and assignment operator welcome.
+
+  // Whether this change is valid. This must be true before attempting to access
+  // the data.
+  // Deletes: Requires valid tag when going to the syncer. Requires valid
+  //          specifics when coming from the syncer.
+  // Adds, Updates: Require valid tag and specifics when going to the syncer.
+  //                Require only valid specifics when coming from the syncer.
+  bool IsValid() const;
+
+  // Getters.
+  SyncChangeType change_type() const;
+  SyncData sync_data() const;
+
+ private:
+  SyncChangeType change_type_;
+
+  // An immutable container for the data of this SyncChange. Whenever
+  // SyncChanges are copied, they copy references to this data.
+  SyncData sync_data_;
+};
+
+#endif  // CHROME_BROWSER_SYNC_API_SYNC_CHANGE_H_