[SyncFS] Add completion callback to PromoteDemotedChanges (1/3)

chrome/browser/sync_file_system/syncable_file_system_util.cc

 // Copyright 2013 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.
 
 #include "chrome/browser/sync_file_system/syncable_file_system_util.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/location.h"
@@ skipping 20 matching lines @@
 
 const char kSyncableMountName[] = "syncfs";
 const char kSyncableMountNameForInternalSync[] = "syncfs-internal";
 
 const base::FilePath::CharType kSyncFileSystemDir[] =
     FILE_PATH_LITERAL("Sync FileSystem");
 
 // Flags to enable features for testing.
 bool g_is_syncfs_v2_enabled = true;
 
+void Noop() {}
+
 }  // namespace
 
 void RegisterSyncableFileSystem() {
   ExternalMountPoints::GetSystemInstance()->RegisterFileSystem(
       kSyncableMountName,
       fileapi::kFileSystemTypeSyncable,
       fileapi::FileSystemMountOption(),
       base::FilePath());
   ExternalMountPoints::GetSystemInstance()->RegisterFileSystem(
       kSyncableMountNameForInternalSync,
@@ skipping 107 matching lines @@
 ScopedDisableSyncFSV2::~ScopedDisableSyncFSV2() {
   DCHECK(!IsV2Enabled());
   g_is_syncfs_v2_enabled = was_enabled_;
 }
 
 void RunSoon(const tracked_objects::Location& from_here,
              const base::Closure& callback) {
   base::MessageLoop::current()->PostTask(from_here, callback);
 }
 
+base::Closure NoopClosure() {
+  return base::Bind(&Noop);
+}
+
 }  // namespace sync_file_system