Sync/Valgrind: Add gmock printers for SyncChange, SyncData, SyncError.

chrome/browser/sync/api/sync_error.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_ERROR_H_
 #define CHROME_BROWSER_SYNC_API_SYNC_ERROR_H_
 #pragma once
 
+#include <iosfwd>
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/sync/syncable/model_type.h"
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 // Sync errors are used for debug purposes and handled internally and/or
@@ skipping 50 matching lines @@
 
   // Reset the error to it's default (unset) values.
   void Clear();
 
   // scoped_ptr is necessary because Location objects aren't assignable.
   scoped_ptr<tracked_objects::Location> location_;
   std::string message_;
   syncable::ModelType type_;
 };
 
+// Printing operator - helps gtest produce readable error messages.
+std::ostream& operator<<(std::ostream& os, const SyncError& sync_error);
+
 #endif  // CHROME_BROWSER_SYNC_API_SYNC_ERROR_H_