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

components/sync/engine_impl/syncer_proto_util_unittest.cc

 // Copyright (c) 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.
 
 #include "components/sync/engine_impl/syncer_proto_util.h"
 
 #include "base/compiler_specific.h"
 #include "base/message_loop/message_loop.h"
 #include "components/sync/base/cancelation_signal.h"
 #include "components/sync/base/model_type_test_util.h"
@@ skipping 230 matching lines @@
   CancelationSignal signal;
   DummyConnectionManager dcm(&signal);
   ClientToServerMessage msg;
   SyncerProtoUtil::SetProtocolVersion(&msg);
   msg.set_share("required");
   msg.set_message_contents(ClientToServerMessage::GET_UPDATES);
   sync_pb::ClientToServerResponse response;
 
   dcm.set_send_error(true);
   EXPECT_FALSE(
-      SyncerProtoUtil::PostAndProcessHeaders(&dcm, NULL, msg, &response));
+      SyncerProtoUtil::PostAndProcessHeaders(&dcm, nullptr, msg, &response));
 
   dcm.set_send_error(false);
   EXPECT_TRUE(
-      SyncerProtoUtil::PostAndProcessHeaders(&dcm, NULL, msg, &response));
+      SyncerProtoUtil::PostAndProcessHeaders(&dcm, nullptr, msg, &response));
 }
 
 }  // namespace syncer