Fix clang-tidy performance warnings in system/tpm. am: 9c6f6b2932 am: 7eb694b2d0
am: 44e6467d30

Change-Id: I4ea107986cf1ac714538ce7ce9b5b658f5e0cbf0
diff --git a/trunks/background_command_transceiver.cc b/trunks/background_command_transceiver.cc
index 51858ca..97255c3 100644
--- a/trunks/background_command_transceiver.cc
+++ b/trunks/background_command_transceiver.cc
@@ -37,7 +37,7 @@
 // A callback which posts another |callback| to a given |task_runner|.
 void PostCallbackToTaskRunner(
     const trunks::CommandTransceiver::ResponseCallback& callback,
-    scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
     const std::string& response) {
   base::Closure task = base::Bind(callback, response);
   task_runner->PostTask(FROM_HERE, task);