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

chrome/browser/devtools/devtools_network_controller_unittest.cc

Index: chrome/browser/devtools/devtools_network_controller_unittest.cc
diff --git a/chrome/browser/devtools/devtools_network_controller_unittest.cc b/chrome/browser/devtools/devtools_network_controller_unittest.cc
index 6893b3ec173951ecd20abd5b173e161eacbab469..ee6684e633456d24f38786bb2506ca0bc83dac1d 100644
--- a/chrome/browser/devtools/devtools_network_controller_unittest.cc
+++ b/chrome/browser/devtools/devtools_network_controller_unittest.cc
@@ -68,7 +68,7 @@ class DevToolsNetworkControllerHelper {
     return request_.get();
   }
 
-  void SetNetworkState(const std::string id, bool offline) {
+  void SetNetworkState(const std::string& id, bool offline) {
     scoped_ptr<DevToolsNetworkConditions> conditions(
         new DevToolsNetworkConditions(offline));
     controller_.SetNetworkState(id, conditions.Pass());