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

chrome/test/chromedriver/capabilities.cc

Index: chrome/test/chromedriver/capabilities.cc
diff --git a/chrome/test/chromedriver/capabilities.cc b/chrome/test/chromedriver/capabilities.cc
index e4ba8638bc6fb7b7e5f0c2273645ad6c28a4c047..bec8f64de9247c7d5d0663b7c78486f9b67359ee 100644
--- a/chrome/test/chromedriver/capabilities.cc
+++ b/chrome/test/chromedriver/capabilities.cc
@@ -97,7 +97,8 @@ Status ParseLogPath(const base::Value& option, Capabilities* capabilities) {
   return Status(kOk);
 }
 
-Status ParseDeviceName(std::string device_name, Capabilities* capabilities) {
+Status ParseDeviceName(const std::string& device_name,
+                       Capabilities* capabilities) {
   scoped_ptr<MobileDevice> device;
   Status status = FindMobileDevice(device_name, &device);