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

components/dom_distiller/core/url_utils_unittest.cc

 // Copyright 2014 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 "components/dom_distiller/core/url_utils.h"
 
 #include "components/dom_distiller/core/url_constants.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "url/gurl.h"
 
@@ skipping 23 matching lines @@
   // Test a valid URL without the key we are searching for.
   const std::string valid_url_no_key = "http://www.google.com";
   EXPECT_EQ("", GetValueForKeyInUrlPathQuery(valid_url_no_key, "key"));
 
   // Test a valid URL with 2 values of the key we are searching for.
   const std::string valid_url_two_keys =
       "http://www.google.com?key=foo&key=bar";
   EXPECT_EQ("foo", GetValueForKeyInUrlPathQuery(valid_url_two_keys, "key"));
 }
 
-std::string ThroughDistiller(std::string url) {
+std::string ThroughDistiller(const std::string& url) {
   return GetOriginalUrlFromDistillerUrl(
       GetDistillerViewUrlFromUrl(kDomDistillerScheme, GURL(url))).spec();
 }
 
-std::string GetOriginalUrlFromDistillerUrl(std::string url) {
+std::string GetOriginalUrlFromDistillerUrl(const std::string& url) {
   return GetOriginalUrlFromDistillerUrl(GURL(url)).spec();
 }
 
 TEST(DomDistillerUrlUtilsTest, TestDistillerEndToEnd) {
   // Tests a normal url.
   const std::string url = "http://example.com/";
   EXPECT_EQ(url, ThroughDistiller(url));
   EXPECT_EQ(url, GetOriginalUrlFromDistillerUrl(url));
 
   // Tests a url with arguments and anchor points.
   const std::string url_arguments =
       "https://example.com/?key=value&key=value2&key2=value3#here";
   EXPECT_EQ(url_arguments, ThroughDistiller(url_arguments));
   EXPECT_EQ(url_arguments, GetOriginalUrlFromDistillerUrl(url_arguments));
 
   // Tests a url with file:// scheme.
   const std::string url_file = "file:///home/userid/path/index.html";
   EXPECT_EQ(url_file, ThroughDistiller(url_file));
   EXPECT_EQ(url_file, GetOriginalUrlFromDistillerUrl(url_file));
 }
 }  // namespace url_utils
 
 }  // namespace dom_distiller