[Sync] Replacing NULL with nullptr in code and null in comments for components/sync/

components/sync/model_impl/attachments/attachment_service_impl.h

 // Copyright 2014 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 COMPONENTS_SYNC_MODEL_IMPL_ATTACHMENTS_ATTACHMENT_SERVICE_IMPL_H_
 #define COMPONENTS_SYNC_MODEL_IMPL_ATTACHMENTS_ATTACHMENT_SERVICE_IMPL_H_
 
 #include <deque>
 #include <memory>
 
@@ skipping 22 matching lines @@
   //
   // |attachment_uploader| is optional. If null, attachments will never be
   // uploaded to the sync server and |delegate|'s OnAttachmentUploaded will
   // never be invoked.
   //
   // |attachment_downloader| is optional. If null, attachments will never be
   // downloaded. Only attachments in |attachment_store| will be returned from
   // GetOrDownloadAttachments.
   //
   // |delegate| is optional delegate for AttachmentService to notify about
-  // asynchronous events (AttachmentUploaded). Pass NULL if delegate is not
+  // asynchronous events (AttachmentUploaded). Pass null if delegate is not
   // provided. AttachmentService doesn't take ownership of delegate, the pointer
   // must be valid throughout AttachmentService lifetime.
   //
   // |initial_backoff_delay| the initial delay between upload attempts.  This
   // class automatically retries failed uploads.  After the first failure, it
   // will wait this amount of time until it tries again.  After each failure,
   // the delay is doubled until the |max_backoff_delay| is reached.  A
   // successful upload clears the delay.
   //
   // |max_backoff_delay| the maxmium delay between upload attempts when backed
@@ skipping 58 matching lines @@
 
   // Must be last data member.
   base::WeakPtrFactory<AttachmentServiceImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AttachmentServiceImpl);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_IMPL_ATTACHMENTS_ATTACHMENT_SERVICE_IMPL_H_