tools/gn: Change auto to not deduce raw pointers.

tools/gn/loader.cc

Index: tools/gn/loader.cc
diff --git a/tools/gn/loader.cc b/tools/gn/loader.cc
index 69fb7668e17dd200c23ec5b37a7f591c5f774d5a..1899df7d556a44130938e048756b7c0b7065d830 100644
--- a/tools/gn/loader.cc
+++ b/tools/gn/loader.cc
@@ -273,7 +273,7 @@ void LoaderImpl::BackgroundLoadFile(const Settings* settings,
 
 
   // Pass all of the items that were defined off to the builder.
-  for (auto& item : collected_items) {
+  for (auto*& item : collected_items) {
     settings->build_settings()->ItemDefined(base::WrapUnique(item));
     item = nullptr;
   }