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

chrome/browser/media/webrtc_browsertest_base.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 "chrome/browser/media/webrtc_browsertest_base.h"
 
 #include "base/lazy_instance.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/media/webrtc_browsertest_common.h"
@@ skipping 315 matching lines @@
       base::StringPrintf("receiveOfferFromPeer('%s', {})", local_offer.c_str());
   std::string response = ExecuteJavascript(javascript, to_tab);
   EXPECT_EQ("ok-", response.substr(0, 3))
       << "Receiving peer failed to receive offer and create answer: "
       << response;
 
   std::string answer = response.substr(3);
   return answer;
 }
 
-void WebRtcTestBase::ReceiveAnswer(std::string answer,
+void WebRtcTestBase::ReceiveAnswer(const std::string& answer,
                                    content::WebContents* from_tab) const {
   ASSERT_EQ(
       "ok-accepted-answer",
       ExecuteJavascript(
           base::StringPrintf("receiveAnswerFromPeer('%s')", answer.c_str()),
           from_tab));
 }
 
 void WebRtcTestBase::GatherAndSendIceCandidates(
     content::WebContents* from_tab,
@@ skipping 66 matching lines @@
 #endif
 }
 
 bool WebRtcTestBase::OnWin8() const {
 #if defined(OS_WIN)
   return base::win::GetVersion() > base::win::VERSION_WIN7;
 #else
   return false;
 #endif
 }