[Sync] Introduce ModelError for USS error handling.

components/sync/model/model_type_sync_bridge.h

Index: components/sync/model/model_type_sync_bridge.h
diff --git a/components/sync/model/model_type_sync_bridge.h b/components/sync/model/model_type_sync_bridge.h
index 8c236ccd70f7678db04b0e540d9846975ceeda2e..bf11f9b1f04ba87fbe53ee53bf719e2f6dc47e20 100644
--- a/components/sync/model/model_type_sync_bridge.h
+++ b/components/sync/model/model_type_sync_bridge.h
@@ -16,8 +16,8 @@
 #include "components/sync/model/data_type_error_handler.h"
 #include "components/sync/model/entity_change.h"
 #include "components/sync/model/entity_data.h"
+#include "components/sync/model/model_error.h"
 #include "components/sync/model/model_type_change_processor.h"
-#include "components/sync/model/sync_error.h"
 
 namespace syncer {
 
@@ -33,8 +33,7 @@ class MetadataChangeList;
 // start calling into the bridge.
 class ModelTypeSyncBridge : public base::SupportsWeakPtr<ModelTypeSyncBridge> {
  public:
-  typedef base::Callback<void(SyncError, std::unique_ptr<DataBatch>)>
-      DataCallback;
+  typedef base::Callback<void(std::unique_ptr<DataBatch>)> DataCallback;
   typedef std::vector<std::string> StorageKeyList;
   typedef base::Callback<std::unique_ptr<ModelTypeChangeProcessor>(
       ModelType type,
@@ -63,7 +62,7 @@ class ModelTypeSyncBridge : public base::SupportsWeakPtr<ModelTypeSyncBridge> {
   // combine all change atomically, should save the metadata after the data
   // changes, so that this merge will be re-driven by sync if is not completely
   // saved during the current run.
-  virtual SyncError MergeSyncData(
+  virtual ModelError MergeSyncData(
       std::unique_ptr<MetadataChangeList> metadata_change_list,
       EntityDataMap entity_data_map) = 0;
 
@@ -72,7 +71,7 @@ class ModelTypeSyncBridge : public base::SupportsWeakPtr<ModelTypeSyncBridge> {
   // |metadata_change_list| in case when some of the data changes are filtered
   // out, or even be empty in case when a commit confirmation is processed and
   // only the metadata needs to persisted.
-  virtual SyncError ApplySyncChanges(
+  virtual ModelError ApplySyncChanges(
       std::unique_ptr<MetadataChangeList> metadata_change_list,
       EntityChangeList entity_changes) = 0;