Cleanup: Pass std::string as const reference from chromeos/

chromeos/dbus/fake_shill_manager_client.h

Index: chromeos/dbus/fake_shill_manager_client.h
diff --git a/chromeos/dbus/fake_shill_manager_client.h b/chromeos/dbus/fake_shill_manager_client.h
index 313a2d43e58e523a7cef3b1f2696c796039399da..f677350d4b7c01d9826d4679a5faa57544430529 100644
--- a/chromeos/dbus/fake_shill_manager_client.h
+++ b/chromeos/dbus/fake_shill_manager_client.h
@@ -126,7 +126,8 @@ class CHROMEOS_EXPORT FakeShillManagerClient
   // {wifi,cellular,etc}={on,off,disabled,none} - sets initial state for type
   void ParseCommandLineSwitch();
   bool ParseOption(const std::string& arg0, const std::string& arg1);
-  bool SetInitialNetworkState(std::string type_arg, std::string state_arg);
+  bool SetInitialNetworkState(std::string type_arg,
+                              const std::string& state_arg);
   std::string GetInitialStateForType(const std::string& type,
                                      bool* enabled);