Cleanup: Pass std::string as const reference if possible

chrome/browser/nacl_host/test/nacl_gdb_browsertest.cc

Index: chrome/browser/nacl_host/test/nacl_gdb_browsertest.cc
diff --git a/chrome/browser/nacl_host/test/nacl_gdb_browsertest.cc b/chrome/browser/nacl_host/test/nacl_gdb_browsertest.cc
index b7d7f4c0230d14a9ddfd86ed76959825a9e1b1c2..6de3fa624d7f8ca336724e79719d76858423235e 100644
--- a/chrome/browser/nacl_host/test/nacl_gdb_browsertest.cc
+++ b/chrome/browser/nacl_host/test/nacl_gdb_browsertest.cc
@@ -34,7 +34,7 @@ class NaClGdbTest : public PPAPINaClNewlibTest {
     command_line->AppendSwitchPath(switches::kNaClGdbScript, script_);
   }
 
-  void RunWithNaClGdb(std::string test_name) {
+  void RunWithNaClGdb(const std::string& test_name) {
     base::FilePath mock_nacl_gdb_file;
     scoped_ptr<base::Environment> env(base::Environment::Create());
     std::string content;