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

net/cookies/cookie_monster_unittest.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 "net/cookies/cookie_store_unittest.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 760 matching lines @@
   // saving the provided callback and sending a quit to the message loop.
   void ExpectLoadCall() {
     EXPECT_CALL(*persistent_store_.get(), Load(testing::_))
         .WillOnce(testing::DoAll(testing::SaveArg<0>(&loaded_callback_),
                                  QuitCurrentMessageLoop()));
   }
 
   // Declares an expectation that PersistentCookieStore::LoadCookiesForKey
   // will be called, saving the provided callback and sending a quit to the
   // message loop.
-  void ExpectLoadForKeyCall(std::string key, bool quit_queue) {
+  void ExpectLoadForKeyCall(const std::string& key, bool quit_queue) {
     if (quit_queue)
       EXPECT_CALL(*persistent_store_.get(), LoadCookiesForKey(key, testing::_))
           .WillOnce(
               testing::DoAll(PushCallbackAction(&loaded_for_key_callbacks_),
                              QuitCurrentMessageLoop()));
     else
       EXPECT_CALL(*persistent_store_.get(), LoadCookiesForKey(key, testing::_))
           .WillOnce(PushCallbackAction(&loaded_for_key_callbacks_));
   }
 
@@ skipping 2259 matching lines @@
       monster()->AddCallbackForCookie(
           test_url_, "abc",
           base::Bind(&RecordCookieChanges, &cookies1, nullptr)));
   SetCookie(monster(), test_url_, "abc=def");
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ(1U, cookies0.size());
   EXPECT_EQ(1U, cookies0.size());
 }
 
 }  // namespace net