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

chrome/browser/sync/test/integration/migration_watcher.cc

Index: chrome/browser/sync/test/integration/migration_watcher.cc
diff --git a/chrome/browser/sync/test/integration/migration_watcher.cc b/chrome/browser/sync/test/integration/migration_watcher.cc
index ab27c4e8169cd0ed3502c64aaf74d79a44cca2bc..17cae9d4be8410e95bc96d25429b28f1075a1def 100644
--- a/chrome/browser/sync/test/integration/migration_watcher.cc
+++ b/chrome/browser/sync/test/integration/migration_watcher.cc
@@ -9,7 +9,7 @@
 #include "components/browser_sync/profile_sync_service.h"
 
 MigrationWatcher::MigrationWatcher(ProfileSyncServiceHarness* harness)
-    : harness_(harness), migration_waiter_(NULL) {
+    : harness_(harness), migration_waiter_(nullptr) {
   syncer::BackendMigrator* migrator =
       harness_->service()->GetBackendMigratorForTest();
   // PSS must have a migrator after sync is setup and initial data type
@@ -62,5 +62,5 @@ void MigrationWatcher::set_migration_waiter(MigrationWaiter* waiter) {
 
 void MigrationWatcher::clear_migration_waiter() {
   DCHECK(migration_waiter_);
-  migration_waiter_ = NULL;
+  migration_waiter_ = nullptr;
 }