Clean up some uses of "auto".

Make actual types more explicit, either by replacing "auto"
with actual type or by assigning std::pair<> elements of
an "auto" variable to typed variables. Avoid binding const
references to temporaries. Avoid copying a container.

Test: m test-art-host-gtest
Change-Id: I1a59f9ba1ee15950cacfc5853bd010c1726de603
diff --git a/compiler/optimizing/codegen_test_utils.h b/compiler/optimizing/codegen_test_utils.h
index 31cd204..00a16fe 100644
--- a/compiler/optimizing/codegen_test_utils.h
+++ b/compiler/optimizing/codegen_test_utils.h
@@ -243,7 +243,7 @@
   GraphChecker graph_checker(graph);
   graph_checker.Run();
   if (!graph_checker.IsValid()) {
-    for (const auto& error : graph_checker.GetErrors()) {
+    for (const std::string& error : graph_checker.GetErrors()) {
       std::cout << error << std::endl;
     }
   }