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

chrome/browser/external_extension_browsertest.cc

 // Copyright (c) 2012 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 "base/command_line.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "components/google/core/browser/google_switches.h"
 #include "components/search_engines/search_engines_pref_names.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/url_constants.h"
 #include "content/public/test/browser_test_utils.h"
 #include "net/test/spawned_test_server/spawned_test_server.h"
 
 namespace {
 
 struct IsSearchProviderTestData {
   IsSearchProviderTestData() : tab(NULL) {}
-  IsSearchProviderTestData(content::WebContents* t, std::string h, GURL url)
-      : tab(t), host(h), test_url(url) {
-  }
+  IsSearchProviderTestData(content::WebContents* t,
+                           const std::string& h,
+                           GURL url)
+      : tab(t), host(h), test_url(url) {}
 
   content::WebContents* tab;
   std::string host;
   GURL test_url;
 };
 
 }  // namespace
 
 class SearchProviderTest : public InProcessBrowserTest {
  protected:
@@ skipping 112 matching lines @@
 IN_PROC_BROWSER_TEST_F(SearchProviderTest,
                        TestIsSearchProviderInstalledWithException) {
   // Change the url for the test page to one that throws an exception when
   // toString is called on the argument given to isSearchProviderInstalled.
   search_provider_test_url_ = test_server()->GetURL(
       "files/is_search_provider_installed_with_exception.html");
 
   FinishIsSearchProviderInstalledTest(StartIsSearchProviderInstalledTest(
       browser(), "www.google.com", ""));
 }