[Sync] Refactor sync datatype error handling.

chrome/browser/sync/api/sync_change_processor.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_PROCESSOR_H_
 #define CHROME_BROWSER_SYNC_API_SYNC_CHANGE_PROCESSOR_H_
 #pragma once
 
 #include <vector>
 
 class SyncChange;
+class SyncError;
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 typedef std::vector<SyncChange> SyncChangeList;
 
 // An interface for services that handle receiving SyncChanges.
 class SyncChangeProcessor {
  public:
   // Process a list of SyncChanges.
-  virtual void ProcessSyncChanges(const tracked_objects::Location& from_here,
-                                  const SyncChangeList& change_list) = 0;
+  // Returns: False if an error occured, true otherwise.
+  // Inputs:
+  //   |from_here|: allows tracking of where sync changes originate.
+  //   |change_list|: is the list of sync changes in need of processing.
+  //   |error|: if an error occurred, the error tracking information.
+  virtual bool ProcessSyncChanges(const tracked_objects::Location& from_here,
+                                  const SyncChangeList& change_list,
+                                  SyncError* error) = 0;
  protected:
   virtual ~SyncChangeProcessor();
 };
 
 
 #endif  // CHROME_BROWSER_SYNC_API_SYNC_CHANGE_PROCESSOR_H_