chromeos: Convert D-Bus client classes' callback arguments to const reference

chromeos/dbus/cashew_client.cc

Index: chromeos/dbus/cashew_client.cc
diff --git a/chromeos/dbus/cashew_client.cc b/chromeos/dbus/cashew_client.cc
index 93d1f3d90aabd1233a4f00f984049986413adbda..eb801f47732e548d9100c114619fc929a743f624 100644
--- a/chromeos/dbus/cashew_client.cc
+++ b/chromeos/dbus/cashew_client.cc
@@ -41,7 +41,7 @@ class CashewClientImpl : public CashewClient {
 
   // CashewClient override.
   virtual void SetDataPlansUpdateHandler(
-      DataPlansUpdateHandler handler) OVERRIDE {
+      const DataPlansUpdateHandler& handler) OVERRIDE {
     data_plans_update_handler_ = handler;
   }
 
@@ -101,7 +101,7 @@ class CashewClientStubImpl : public CashewClient {
 
   // CashewClient override.
   virtual void SetDataPlansUpdateHandler(
-      DataPlansUpdateHandler handler) OVERRIDE {}
+      const DataPlansUpdateHandler& handler) OVERRIDE {}
 
   // CashewClient override.
   virtual void ResetDataPlansUpdateHandler() OVERRIDE {}