[SyncFS] Use nullptr instead of NULL

chrome/browser/sync_file_system/local/local_file_change_tracker_unittest.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/local/local_file_change_tracker.h"
 
 #include <deque>
 #include <set>
 
 #include "base/basictypes.h"
@@ skipping 41 matching lines @@
                                  base::ThreadTaskRunnerHandle::Get().get(),
                                  base::ThreadTaskRunnerHandle::Get().get());
     ASSERT_EQ(
         sync_file_system::SYNC_STATUS_OK,
         file_system_.MaybeInitializeFileSystemContext(sync_context_.get()));
   }
 
   virtual void TearDown() OVERRIDE {
     if (sync_context_.get())
       sync_context_->ShutdownOnUIThread();
-    sync_context_ = NULL;
+    sync_context_ = nullptr;
 
     message_loop_.RunUntilIdle();
     file_system_.TearDown();
     // Make sure we don't leave the external filesystem.
     // (CannedSyncableFileSystem::TearDown does not do this as there may be
     // multiple syncable file systems registered for the name)
     RevokeSyncableFileSystem();
   }
 
  protected:
@@ skipping 632 matching lines @@
 
   // Make sure they're gone from the database too.
   DropChangesInTracker();
   RestoreChangesFromTrackerDB();
 
   GetAllChangedURLs(&urls);
   EXPECT_TRUE(urls.empty());
 }
 
 }  // namespace sync_file_system