sync: Improve handling of bad UniquePos (retry)

sync/internal_api/public/base/unique_position.h

 // Copyright (c) 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_UNIQUE_POSITION_H_
 #define SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 28 matching lines @@
 // This class currently has several bookmarks-related assumptions built in,
 // though it could be adapted to be more generally useful.
 class SYNC_EXPORT_PRIVATE UniquePosition {
  public:
   static const size_t kSuffixLength;
   static const size_t kCompressBytesThreshold;
 
   static bool IsValidSuffix(const std::string& suffix);
   static bool IsValidBytes(const std::string& bytes);
 
+  // Returns a valid, but mostly random suffix.
+  // Avoid using this; it can lead to inconsistent sort orderings if misused.
+  static std::string RandomSuffix();
+
   // Returns an invalid position.
   static UniquePosition CreateInvalid();
 
   // Converts from a 'sync_pb::UniquePosition' protobuf to a UniquePosition.
   // This may return an invalid position if the parsing fails.
   static UniquePosition FromProto(const sync_pb::UniquePosition& proto);
 
   // Creates a position with the given suffix.  Ordering among positions created
   // from this function is the same as that of the integer parameters that were
   // passed in.
@@ skipping 72 matching lines @@
 
   // The position value after it has been run through the custom compression
   // algorithm.  See Compress() and Uncompress() functions above.
   std::string compressed_;
   bool is_valid_;
 };
 
 }  // namespace syncer;
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_