ART: Fix reference-related warnings

Make some parameters and locals references to avoid unnecessary
copies.

Bug: 32619234
Test: m test-art-host
Change-Id: Idfed600c7c5492a80f72f51424253bcbea824a94
diff --git a/profman/profile_assistant_test.cc b/profman/profile_assistant_test.cc
index c78d34e..8cbf8c3 100644
--- a/profman/profile_assistant_test.cc
+++ b/profman/profile_assistant_test.cc
@@ -207,7 +207,7 @@
     return ExecAndReturnCode(argv_str, &error);
   }
 
-  bool CreateProfile(std::string profile_file_contents,
+  bool CreateProfile(const std::string& profile_file_contents,
                      const std::string& filename,
                      const std::string& dex_location) {
     ScratchFile class_names_file;