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

extensions/browser/guest_view/web_view/web_view_renderer_state.h

 // 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.
 
 // WebViewRendererState manages state data for WebView guest renderer processes.
 //
 // This class's data can be accessed via its methods from both the UI and IO
 // threads, and uses locks to mediate this access. When making changes to this
 // class, ensure that you avoid introducing any reentrant code in the methods,
 // and that you always aquire the locks in the order |web_view_info_map_lock_|
@@ skipping 63 matching lines @@
   friend class WebViewGuest;
   friend struct base::DefaultSingletonTraits<WebViewRendererState>;
 
   using RenderId = std::pair<int, int>;
   using WebViewInfoMap = std::map<RenderId, WebViewInfo>;
 
   struct WebViewPartitionInfo {
     int web_view_count;
     std::string partition_id;
     WebViewPartitionInfo() {}
-    WebViewPartitionInfo(int count, std::string partition):
-      web_view_count(count),
-      partition_id(partition) {}
+    WebViewPartitionInfo(int count, const std::string& partition)
+        : web_view_count(count), partition_id(partition) {}
   };
 
   using WebViewPartitionIDMap = std::map<int, WebViewPartitionInfo>;
 
   WebViewRendererState();
   ~WebViewRendererState();
 
   // Adds/removes a WebView guest render process to/from the set.
   void AddGuest(int render_process_host_id, int routing_id,
                 const WebViewInfo& web_view_info);
   void RemoveGuest(int render_process_host_id, int routing_id);
 
   // Locks are used to mediate access to these maps from both the UI and IO
   // threads.
   WebViewInfoMap web_view_info_map_;
   mutable base::Lock web_view_info_map_lock_;
   WebViewPartitionIDMap web_view_partition_id_map_;
   mutable base::Lock web_view_partition_id_map_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(WebViewRendererState);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_GUEST_VIEW_WEB_VIEW_WEB_VIEW_RENDERER_STATE_H_