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

net/tools/tld_cleanup/tld_cleanup_util_unittest.cc

 // Copyright 2013 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/tools/tld_cleanup/tld_cleanup_util.h"
 
 #include "base/files/file_path.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
 namespace tld_cleanup {
 
-std::string SetupData(std::string icann_domains, std::string private_domains) {
+std::string SetupData(const std::string& icann_domains,
+                      const std::string& private_domains) {
   return "// ===BEGIN ICANN DOMAINS===\n" +
          icann_domains +
          "// ===END ICANN DOMAINS===\n" +
          "// ===BEGIN PRIVATE DOMAINS===\n" +
          private_domains +
          "// ===END PRIVATE DOMAINS===\n";
 }
 
 TEST(TldCleanupUtilTest, TwoRealTldsSuccessfullyRead) {
   std::string icann_domains = "foo\n"
@@ skipping 134 matching lines @@
   EXPECT_FALSE(bar_iter->second.is_private);
   RuleMap::const_iterator baz_bar_iter = rules.find("baz.bar");
   ASSERT_FALSE(rules.end() == baz_bar_iter);
   EXPECT_FALSE(baz_bar_iter->second.wildcard);
   EXPECT_TRUE(baz_bar_iter->second.exception);
   EXPECT_TRUE(baz_bar_iter->second.is_private);
 }
 
 }  // namespace tld_cleanup
 }  // namespace net