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

components/sync/engine/sync_manager.cc

Index: components/sync/engine/sync_manager.cc
diff --git a/components/sync/engine/sync_manager.cc b/components/sync/engine/sync_manager.cc
index 34cba6205c37ea7ca02ff431585759973af2c65a..90fa6b73ac6de67e1a76626b3427322c800b429b 100644
--- a/components/sync/engine/sync_manager.cc
+++ b/components/sync/engine/sync_manager.cc
@@ -19,10 +19,10 @@ SyncManager::ChangeObserver::~ChangeObserver() {}
 SyncManager::Observer::~Observer() {}
 
 SyncManager::InitArgs::InitArgs()
-    : extensions_activity(NULL),
-      change_delegate(NULL),
-      encryptor(NULL),
-      cancelation_signal(NULL) {}
+    : extensions_activity(nullptr),
+      change_delegate(nullptr),
+      encryptor(nullptr),
+      cancelation_signal(nullptr) {}
 
 SyncManager::InitArgs::~InitArgs() {}