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

components/sync/driver/generic_change_processor_unittest.cc

Index: components/sync/driver/generic_change_processor_unittest.cc
diff --git a/components/sync/driver/generic_change_processor_unittest.cc b/components/sync/driver/generic_change_processor_unittest.cc
index e4f74d78b99d5ccb317d29f7a9c2d497c125e362..96ddee15acfa8093f728cfec50a602ffecfe21ab 100644
--- a/components/sync/driver/generic_change_processor_unittest.cc
+++ b/components/sync/driver/generic_change_processor_unittest.cc
@@ -125,7 +125,7 @@ class SyncGenericChangeProcessorTest : public testing::Test {
 
   SyncGenericChangeProcessorTest()
       : syncable_service_ptr_factory_(&fake_syncable_service_),
-        mock_attachment_service_(NULL),
+        mock_attachment_service_(nullptr),
         sync_client_(&sync_factory_) {}
 
   void SetUp() override {
@@ -136,7 +136,7 @@ class SyncGenericChangeProcessorTest : public testing::Test {
   }
 
   void TearDown() override {
-    mock_attachment_service_ = NULL;
+    mock_attachment_service_ = nullptr;
     if (test_user_share_) {
       test_user_share_->TearDown();
     }