[background-sync] Remove WebSyncError and SyncCallbacks

third_party/WebKit/public/platform/modules/background_sync/WebSyncError.h

-// Copyright 2015 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 WebSyncError_h
-#define WebSyncError_h
-
-#include "public/platform/WebString.h"
-
-namespace blink {
-
-struct WebSyncError {
-  enum ErrorType {
-    ErrorTypeAbort = 0,
-    ErrorTypeNoPermission,
-    ErrorTypeNotFound,
-    ErrorTypePermissionDenied,
-    ErrorTypeUnknown,
-    ErrorTypeLast = ErrorTypeUnknown
-  };
-
-  WebSyncError(ErrorType errorType, const WebString& message)
-      : errorType(errorType), message(message) {}
-
-  ErrorType errorType;
-  WebString message;
-};
-
-}  // namespace blink
-
-#endif  // WebSyncError_h