Add version field to syncer::Invalidation.

sync/internal_api/public/base/invalidation.h

 // Copyright 2012 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 SYNC_INTERNAL_API_PUBLIC_BASE_INVALIDATION_H_
 #define SYNC_INTERNAL_API_PUBLIC_BASE_INVALIDATION_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 25 matching lines @@
 
  private:
   // Explicitly copyable and assignable for STL containers.
   AckHandle(const std::string& state, base::Time timestamp);
 
   std::string state_;
   base::Time timestamp_;
 };
 
 // Represents a local invalidation, and is roughly analogous to
-// invalidation::Invalidation. It contains a payload (which may be empty) and an
+// invalidation::Invalidation. It contains a version (which may be
+// kUnknownVersion), a payload (which may be empty) and an
 // associated ack handle that an InvalidationHandler implementation can use to
 // acknowledge receipt of the invalidation. It does not embed the object ID,
 // since it is typically associated with it through ObjectIdInvalidationMap.
 struct SYNC_EXPORT Invalidation {
+  static const int64 kUnknownVersion;
+
   Invalidation();
   ~Invalidation();
 
   bool Equals(const Invalidation& other) const;
 
   scoped_ptr<base::DictionaryValue> ToValue() const;
   bool ResetFromValue(const base::DictionaryValue& value);
 
+  int64 version;
   std::string payload;
   AckHandle ack_handle;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_BASE_INVALIDATION_H_