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

chrome/browser/extensions/isolated_app_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/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/extensions/extension_apitest.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_commands.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
@@ skipping 84 matching lines @@
     for (size_t i = 0; i < cookies_to_set.size(); i++)
       http_response->AddCustomHeader("Set-Cookie", cookies_to_set[i]);
   }
 
   return http_response.Pass();
 }
 
 class IsolatedAppTest : public ExtensionBrowserTest {
  public:
   // Returns whether the given tab's current URL has the given cookie.
-  bool WARN_UNUSED_RESULT HasCookie(WebContents* contents, std::string cookie) {
+  bool WARN_UNUSED_RESULT HasCookie(WebContents* contents,
+                                    const std::string& cookie) {
     int value_size;
     std::string actual_cookie;
     ui_test_utils::GetCookies(contents->GetURL(), contents, &value_size,
                               &actual_cookie);
     return actual_cookie.find(cookie) != std::string::npos;
   }
 
   const Extension* GetInstalledApp(WebContents* contents) {
     content::BrowserContext* browser_context = contents->GetBrowserContext();
     ExtensionRegistry* registry = ExtensionRegistry::Get(browser_context);
@@ skipping 443 matching lines @@
       browser(), base_url.Resolve("non_app/main.html"));
   ASSERT_TRUE(ExecuteScriptAndExtractString(
       browser()->tab_strip_model()->GetWebContentsAt(0),
       kRetrieveSessionStorage.c_str(), &result));
   EXPECT_EQ("ss_normal", result);
 }
 
 }  // namespace
 
 }  // namespace extensions