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

ipc/ipc_sync_message_unittest.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Unit test to make sure that the serialization of synchronous IPC messages
 // works.  This ensures that the macros and templates were defined correctly.
 // Doesn't test the IPC channel mechanism.
 
 #include "base/logging.h"
 #include "ipc/ipc_message.h"
@@ skipping 57 matching lines @@
   }
 
   void On_2_3(int in1, bool in2, std::string* out1, int* out2, bool* out3) {
     DCHECK_EQ(3, in1);
     DCHECK(in2);
     *out1 = "2_3";
     *out2 = 23;
     *out3 = false;
   }
 
-  void On_3_1(int in1, bool in2, std::string in3, bool* out1) {
+  void On_3_1(int in1, bool in2, const std::string& in3, bool* out1) {
     DCHECK_EQ(1, in1);
     DCHECK(!in2);
     DCHECK_EQ("3_1", in3);
     *out1 = true;
   }
 
-  void On_3_2(std::string in1, bool in2, int in3, bool* out1, int* out2) {
+  void On_3_2(const std::string& in1,
+              bool in2,
+              int in3,
+              bool* out1,
+              int* out2) {
     DCHECK_EQ("3_2", in1);
     DCHECK(!in2);
     DCHECK_EQ(2, in3);
     *out1 = true;
     *out2 = 32;
   }
 
-  void On_3_3(int in1, std::string in2, bool in3, std::string* out1, int* out2,
+  void On_3_3(int in1,
+              const std::string& in2,
+              bool in3,
+              std::string* out1,
+              int* out2,
               bool* out3) {
     DCHECK_EQ(3, in1);
     DCHECK_EQ("3_3", in2);
     DCHECK(in3);
     *out1 = "3_3";
     *out2 = 33;
     *out3 = false;
   }
 
-  void On_3_4(bool in1, int in2, std::string in3, int* out1, bool* out2,
-              std::string* out3, bool* out4) {
+  void On_3_4(bool in1,
+              int in2,
+              const std::string& in3,
+              int* out1,
+              bool* out2,
+              std::string* out3,
+              bool* out4) {
     DCHECK(in1);
     DCHECK_EQ(3, in2);
     DCHECK_EQ("3_4", in3);
     *out1 = 34;
     *out2 = true;
     *out3 = "3_4";
     *out4 = false;
   }
 
   bool Send(IPC::Message* message) {
@@ skipping 180 matching lines @@
   DCHECK_EQ(32, int1);
 
   bool1 = true;
   Send(new Msg_R_3_3(0, 3, "3_3", true, &string1, &int1, &bool1));
   DCHECK_EQ("3_3", string1);
   DCHECK_EQ(33, int1);
   DCHECK(!bool1);
 }
 
 }  // namespace