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

components/sync/driver/about_sync_util_unittest.cc

Index: components/sync/driver/about_sync_util_unittest.cc
diff --git a/components/sync/driver/about_sync_util_unittest.cc b/components/sync/driver/about_sync_util_unittest.cc
index e55fee5bf68fae512cad53941e1484d35f7cbb6f..7a6effb2467c40d8d5206e5b624347ff7c722a55 100644
--- a/components/sync/driver/about_sync_util_unittest.cc
+++ b/components/sync/driver/about_sync_util_unittest.cc
@@ -39,7 +39,7 @@ TEST(SyncUIUtilTestAbout, ConstructAboutInformationWithUnrecoverableErrorTest) {
   SyncServiceMock service;
 
   std::unique_ptr<base::DictionaryValue> strings(ConstructAboutInformation(
-      &service, NULL, version_info::Channel::UNKNOWN));
+      &service, nullptr, version_info::Channel::UNKNOWN));
 
   EXPECT_TRUE(strings->HasKey("unrecoverable_error_detected"));
 }