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

tools/gn/scope.cc

Index: tools/gn/scope.cc
diff --git a/tools/gn/scope.cc b/tools/gn/scope.cc
index 93ce966e4f3e8abfcb0bc20ce9e7a374ed56f9a5..3869f3b42921c261f70e28658de6665c2053d732 100644
--- a/tools/gn/scope.cc
+++ b/tools/gn/scope.cc
@@ -69,7 +69,7 @@ Scope::~Scope() {
 const Value* Scope::GetValue(const base::StringPiece& ident,
                              bool counts_as_used) {
   // First check for programmatically-provided values.
-  for (const auto& provider : programmatic_providers_) {
+  for (auto* provider : programmatic_providers_) {
     const Value* v = provider->GetProgrammaticValue(ident);
     if (v)
       return v;