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

media/cast/test/utility/input_builder.h

 // Copyright 2014 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.
 
 #ifndef MEDIA_CAST_TEST_UTILITY_INPUT_BUILDER_
 #define MEDIA_CAST_TEST_UTILITY_INPUT_BUILDER_
 
 #include <string>
 
 namespace media {
@@ skipping 15 matching lines @@
   // Ask the user for input, reads input from the input source and returns
   // the answer. This method will keep asking the user until a correct answer
   // is returned and is thereby guaranteed to return a response that is
   // acceptable within the predefined range.
   // Input will be returned in either string or int format, base on the function
   // called.
   std::string GetStringInput() const;
   int GetIntInput() const;
 
  private:
-  bool ValidateInput(const std::string input) const;
+  bool ValidateInput(const std::string& input) const;
 
   const std::string title_;
   const std::string default_value_;
   // Low and high range values for input validation.
   const int low_range_;
   const int high_range_;
 };
 
 }  // namespace test
 }  // namespace cast
 }  // namespace media
 
 #endif  // MEDIA_CAST_TEST_UTILITY_INPUT_BUILDER_