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

components/browser_sync/profile_sync_service.h

 // 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.
 
 #ifndef COMPONENTS_BROWSER_SYNC_PROFILE_SYNC_SERVICE_H_
 #define COMPONENTS_BROWSER_SYNC_PROFILE_SYNC_SERVICE_H_
 
 #include <memory>
 #include <set>
 #include <string>
@@ skipping 450 matching lines @@
 
   // TODO(akalin): These two functions are used only by
   // ProfileSyncServiceHarness.  Figure out a different way to expose
   // this info to that class, and remove these functions.
 
   // Returns whether or not the underlying sync engine has made any
   // local changes to items that have not yet been synced with the
   // server.
   bool HasUnsyncedItems() const;
 
-  // Used by ProfileSyncServiceHarness.  May return NULL.
+  // Used by ProfileSyncServiceHarness.  May return null.
   syncer::BackendMigrator* GetBackendMigratorForTest();
 
   // Used by tests to inspect interaction with OAuth2TokenService.
   bool IsRetryingAccessTokenFetchForTest() const;
 
   // Used by tests to inspect the OAuth2 access tokens used by PSS.
   std::string GetAccessTokenForTest() const;
 
   // TODO(sync): This is only used in tests.  Can we remove it?
   void GetModelSafeRoutingInfo(syncer::ModelSafeRoutingInfo* out) const;
@@ skipping 526 matching lines @@
   base::WeakPtrFactory<ProfileSyncService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ProfileSyncService);
 };
 
 bool ShouldShowActionOnUI(const syncer::SyncProtocolError& error);
 
 }  // namespace browser_sync
 
 #endif  // COMPONENTS_BROWSER_SYNC_PROFILE_SYNC_SERVICE_H_