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

chrome/browser/sync/api/sync_data.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_DATA_H_
 #define CHROME_BROWSER_SYNC_API_SYNC_DATA_H_
 #pragma once
 
+#include <iosfwd>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "chrome/browser/sync/syncable/model_type.h"
 #include "chrome/browser/sync/util/immutable.h"
 
 namespace sync_pb {
 class EntitySpecifics;
 class SyncEntity;
@@ skipping 85 matching lines @@
   // Whether this SyncData holds valid data.
   bool is_valid_;
 
   // Equal to sync_api::kInvalidId iff this is local.
   int64 id_;
 
   // The actual shared sync entity being held.
   ImmutableSyncEntity immutable_entity_;
 };
 
+// Printing operator - helps gtest produce readable error messages.
+std::ostream& operator<<(std::ostream& os, const SyncData& sync_data);
+
 #endif  // CHROME_BROWSER_SYNC_API_SYNC_DATA_H_