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

components/sync/driver/ui_data_type_controller_unittest.cc

Index: components/sync/driver/ui_data_type_controller_unittest.cc
diff --git a/components/sync/driver/ui_data_type_controller_unittest.cc b/components/sync/driver/ui_data_type_controller_unittest.cc
index b8234b0aad8266e82937c376b3cfc9b248b7aedc..39b3a2f71a251f1e4f9d2669ef34acef33c98a59 100644
--- a/components/sync/driver/ui_data_type_controller_unittest.cc
+++ b/components/sync/driver/ui_data_type_controller_unittest.cc
@@ -48,7 +48,7 @@ class SyncUIDataTypeControllerTest : public testing::Test,
                                      public FakeSyncClient {
  public:
   SyncUIDataTypeControllerTest()
-      : type_(PREFERENCES), change_processor_(NULL) {}
+      : type_(PREFERENCES), change_processor_(nullptr) {}
 
   // FakeSyncClient overrides.
   base::WeakPtr<SyncableService> GetSyncableServiceForType(
@@ -65,7 +65,7 @@ class SyncUIDataTypeControllerTest : public testing::Test,
   void TearDown() override {
     // Must be done before we pump the loop.
     syncable_service_.StopSyncing(type_);
-    preference_dtc_ = NULL;
+    preference_dtc_ = nullptr;
     PumpLoop();
   }