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

components/search_engines/template_url_parser_unittest.cc

Index: components/search_engines/template_url_parser_unittest.cc
diff --git a/components/search_engines/template_url_parser_unittest.cc b/components/search_engines/template_url_parser_unittest.cc
index ea94a51f2f2550c4ddcd73f64d3c4a5d5354a9a9..1e7dc02b19f105a5a43161fab4e3913bc070c97f 100644
--- a/components/search_engines/template_url_parser_unittest.cc
+++ b/components/search_engines/template_url_parser_unittest.cc
@@ -20,7 +20,7 @@ using base::ASCIIToUTF16;
 // occurrence of value_str_ in its value.
 class ParamFilterImpl : public TemplateURLParser::ParameterFilter {
  public:
-  ParamFilterImpl(std::string name_str, std::string value_str);
+  ParamFilterImpl(const std::string& name_str, const std::string& value_str);
   ~ParamFilterImpl() override;
 
   bool KeepParameter(const std::string& key, const std::string& value) override;
@@ -32,10 +32,9 @@ class ParamFilterImpl : public TemplateURLParser::ParameterFilter {
   DISALLOW_COPY_AND_ASSIGN(ParamFilterImpl);
 };
 
-ParamFilterImpl::ParamFilterImpl(std::string name_str, std::string value_str)
-   : name_str_(name_str),
-     value_str_(value_str) {
-}
+ParamFilterImpl::ParamFilterImpl(const std::string& name_str,
+                                 const std::string& value_str)
+    : name_str_(name_str), value_str_(value_str) {}
 
 ParamFilterImpl::~ParamFilterImpl() {
 }