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

remoting/host/native_messaging/native_messaging_reader_unittest.cc

Index: remoting/host/native_messaging/native_messaging_reader_unittest.cc
diff --git a/remoting/host/native_messaging/native_messaging_reader_unittest.cc b/remoting/host/native_messaging/native_messaging_reader_unittest.cc
index 38728b1a624845e96c9aa0545005d3af22206ae5..4a22ec827cd5b1ff56adf7997d3d375a7f3d0476 100644
--- a/remoting/host/native_messaging/native_messaging_reader_unittest.cc
+++ b/remoting/host/native_messaging/native_messaging_reader_unittest.cc
@@ -30,7 +30,7 @@ class NativeMessagingReaderTest : public testing::Test {
   void OnMessage(scoped_ptr<base::Value> message);
 
   // Writes a message (header+body) to the write-end of the pipe.
-  void WriteMessage(std::string message);
+  void WriteMessage(const std::string& message);
 
   // Writes some data to the write-end of the pipe.
   void WriteData(const char* data, int length);
@@ -74,7 +74,7 @@ void NativeMessagingReaderTest::OnMessage(scoped_ptr<base::Value> message) {
   message_ = message.Pass();
 }
 
-void NativeMessagingReaderTest::WriteMessage(std::string message) {
+void NativeMessagingReaderTest::WriteMessage(const std::string& message) {
   uint32 length = message.length();
   WriteData(reinterpret_cast<char*>(&length), 4);
   WriteData(message.data(), length);