sync: add a SyncSessionJobPurpose for clearing sync user data.

chrome/browser/sync/engine/nudge_source.h

 // Copyright (c) 2010 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_ENGINE_NUDGE_SOURCE_H_
 #define CHROME_BROWSER_SYNC_ENGINE_NUDGE_SOURCE_H_
 #pragma once
 
 namespace browser_sync {
 
 namespace s3 {
 
 enum NudgeSource {
   NUDGE_SOURCE_UNKNOWN = 0,
   // We received an invalidation message and are nudging to check for updates.
   NUDGE_SOURCE_NOTIFICATION,
   // A local change occurred (e.g. bookmark moved).
   NUDGE_SOURCE_LOCAL,
   // A previous sync cycle did not fully complete (e.g. HTTP error).
   NUDGE_SOURCE_CONTINUATION,
-  // A nudge corresponding to the user invoking a function in the UI to clear
-  // their entire account and stop syncing (globally).
-  NUDGE_SOURCE_CLEAR_PRIVATE_DATA,
 };
 
 }  // namespace s3
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_NUDGE_SOURCE_H_