[Sync] Replacing NULL with nullptr/null throughout sync code.

chrome/browser/sync/sync_global_error.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 "chrome/browser/sync/sync_global_error.h"
 
 #include "chrome/app/chrome_command_ids.h"
 #include "chrome/browser/sync/sync_ui_util.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_commands.h"
@@ skipping 24 matching lines @@
 
 SyncGlobalError::~SyncGlobalError() {
   DCHECK(!error_controller_)
       << "SyncGlobalError::Shutdown() was not called";
 }
 
 void SyncGlobalError::Shutdown() {
   if (!switches::IsMaterialDesignUserMenu())
     global_error_service_->RemoveGlobalError(this);
   error_controller_->RemoveObserver(this);
-  error_controller_ = NULL;
+  error_controller_ = nullptr;
 }
 
 bool SyncGlobalError::HasMenuItem() {
   return !menu_label_.empty();
 }
 
 int SyncGlobalError::MenuItemCommandID() {
   return IDC_SHOW_SYNC_ERROR;
 }
 
@@ skipping 59 matching lines @@
 
   if (menu_label != menu_label_ || bubble_message != bubble_message_ ||
       bubble_accept_label != bubble_accept_label_) {
     menu_label_ = menu_label;
     bubble_message_ = bubble_message;
     bubble_accept_label_ = bubble_accept_label;
 
     global_error_service_->NotifyErrorsChanged(this);
   }
 }