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

media/cast/test/utility/input_builder.cc

Index: media/cast/test/utility/input_builder.cc
diff --git a/media/cast/test/utility/input_builder.cc b/media/cast/test/utility/input_builder.cc
index 6fbe5064d850a02222cad5b1a24d00f99020a8db..c0b75db5ae07bffe3eed4a24d99ba574cc6e8589 100644
--- a/media/cast/test/utility/input_builder.cc
+++ b/media/cast/test/utility/input_builder.cc
@@ -63,7 +63,7 @@ int InputBuilder::GetIntInput() const {
   return int_value;
 }
 
-bool InputBuilder::ValidateInput(const std::string input) const {
+bool InputBuilder::ValidateInput(const std::string& input) const {
   // Check for a valid range.
   if (low_range_ == INT_MIN && high_range_ == INT_MAX)
     return true;