[Sync] Update SyncBackendHost to forward ClearServerData to SyncManager

sync/internal_api/public/sync_manager.h

 // Copyright 2012 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 SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_H_
 #define SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 260 matching lines @@
     CancelationSignal* cancelation_signal;
 
     // Optional nigori state to be restored.
     scoped_ptr<SyncEncryptionHandler::NigoriState> saved_nigori_state;
 
     // Whether sync should clear server data when transitioning to passphrase
     // encryption.
     PassphraseTransitionClearDataOption clear_data_option;
   };
 
+  typedef base::Callback<void(void)> ClearServerDataCallback;
+
   SyncManager();
   virtual ~SyncManager();
 
   // Initialize the sync manager using arguments from |args|.
   //
   // Note, args is passed by non-const pointer because it contains objects like
   // scoped_ptr.
   virtual void Init(InitArgs* args) = 0;
 
   virtual ModelTypeSet InitialSyncEndedTypes() = 0;
@@ skipping 102 matching lines @@
   virtual void RegisterDirectoryTypeDebugInfoObserver(
       syncer::TypeDebugInfoObserver* observer) = 0;
   virtual void UnregisterDirectoryTypeDebugInfoObserver(
       syncer::TypeDebugInfoObserver* observer) = 0;
   virtual bool HasDirectoryTypeDebugInfoObserver(
       syncer::TypeDebugInfoObserver* observer) = 0;
 
   // Request that all current counter values be emitted as though they had just
   // been updated.  Useful for initializing new observers' state.
   virtual void RequestEmitDebugInfo() = 0;
+
+  // Clears server data and invokes |callback| when complete.
+  //
+  // This is an asynchronous operation that requires interaction with the sync
+  // server. The operation will automatically be retried with backoff until it
+  // completes successfully or sync is shutdown.
+  virtual void ClearServerData(const ClearServerDataCallback& callback) = 0;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_H_