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

chrome/browser/safe_browsing/client_side_model_loader.h

 // 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.
 //
 // Helper class loads models for client-side phishing detection
 // from the the SafeBrowsing backends.
 //
 // This class is not thread-safe and expects all calls to be made on the UI
 // thread.
 
@@ skipping 65 matching lines @@
     MODEL_EMPTY,
     MODEL_TOO_LARGE,
     MODEL_PARSE_ERROR,
     MODEL_MISSING_FIELDS,
     MODEL_INVALID_VERSION_NUMBER,
     MODEL_BAD_HASH_IDS,
     MODEL_STATUS_MAX  // Always add new values before this one.
   };
 
   // For testing only.
-  ModelLoader(base::Closure update_renderers, const std::string model_name);
+  ModelLoader(base::Closure update_renderers, const std::string& model_name);
 
   // This is called periodically to check whether a new client model is
   // available for download.
   virtual void StartFetch();
 
   // This method is called when we're done fetching the model either because
   // we hit an error somewhere or because we're actually done fetch and
   // validating the model.  If |max_age| is not 0, it's used to schedule the
   // next fetch.
   virtual void EndFetch(ClientModelStatus status, base::TimeDelta max_age);
@@ skipping 37 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(ModelLoaderTest, RescheduleFetchTest);
   FRIEND_TEST_ALL_PREFIXES(ModelLoaderTest, UpdateRenderersTest);
   FRIEND_TEST_ALL_PREFIXES(ClientSideDetectionServiceTest,
                            SetEnabledAndRefreshState);
   DISALLOW_COPY_AND_ASSIGN(ModelLoader);
 };
 
 }  // namespace safe_browsing
 
 #endif  // CHROME_BROWSER_SAFE_BROWSING_CLIENT_SIDE_MODEL_LOADER_H_