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

net/cert/internal/parse_certificate_unittest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/cert/internal/parse_certificate.h"
 
 #include "base/strings/stringprintf.h"
 #include "net/cert/internal/test_helpers.h"
 #include "net/der/input.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
 
 namespace {
 
 // Pretty-prints a GeneralizedTime as a human-readable string for use in test
 // expectations (it is more readable to specify the expected results as a
 // string).
 std::string ToString(const der::GeneralizedTime& time) {
   return base::StringPrintf(
       "year=%d, month=%d, day=%d, hours=%d, minutes=%d, seconds=%d", time.year,
       time.month, time.day, time.hours, time.minutes, time.seconds);
 }
 
-std::string GetFilePath(const std::string file_name) {
+std::string GetFilePath(const std::string& file_name) {
   return std::string("net/data/parse_certificate_unittest/") + file_name;
 }
 
 // Loads certificate data and expectations from the PEM file |file_name|.
 // Verifies that parsing the Certificate succeeds, and each parsed field matches
 // the expectations.
 void EnsureParsingCertificateSucceeds(const std::string& file_name) {
   std::string data;
   std::string expected_tbs_certificate;
   std::string expected_signature_algorithm;
@@ skipping 286 matching lines @@
 
 // Parses a TBSCertificate whose "validity" field does not strictly follow
 // the DER rules (and fails to be parsed).
 TEST(ParseTbsCertificateTest, ValidityRelaxed) {
   EnsureParsingTbsFails("tbs_validity_relaxed.pem");
 }
 
 }  // namespace
 
 }  // namespace net