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

chrome/browser/net/sdch_browsertest.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.
 
 // End-to-end SDCH tests.  Uses the embedded test server to return SDCH
 // results
 
 #include "base/base64.h"
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 113 matching lines @@
   std::replace(output->begin(), output->end(), '+', '-');
   std::replace(output->begin(), output->end(), '/', '_');
 }
 
 // Class that bundles responses for an EmbeddedTestServer().
 // Dictionary is at <domain>/dict, data at <domain>/data.
 // The data is sent SDCH encoded if that's allowed by protoocol.
 class SdchResponseHandler {
  public:
   // Do initial preparation so that SDCH requests can be handled.
-  explicit SdchResponseHandler(std::string domain)
-      : cache_sdch_response_(false),
-        weak_ptr_factory_(this) {
+  explicit SdchResponseHandler(const std::string& domain)
+      : cache_sdch_response_(false), weak_ptr_factory_(this) {
     // Dictionary
     sdch_dictionary_contents_ = "Domain: ";
     sdch_dictionary_contents_ += domain;
     sdch_dictionary_contents_ += "\n\n";
     sdch_dictionary_contents_ += kDictionaryContents;
 
     // Dictionary hash for client and server.
     char binary_hash[32];
     crypto::SHA256HashString(sdch_dictionary_contents_, binary_hash,
                              sizeof(binary_hash));
@@ skipping 560 matching lines @@
   ASSERT_TRUE(SetupIncognitoBrowser());
   ASSERT_TRUE(ForceSdchDictionaryLoad(incognito_browser()));
 
   // Data fetches on main browser should not be SDCH encoded.
   bool sdch_encoding_used = true;
   ASSERT_TRUE(GetData(&sdch_encoding_used));
   EXPECT_FALSE(sdch_encoding_used);
 }
 
 }  // namespace