treewide: Clean up string parameters

Change-Id: I0d3ea6a83465181d3edec1587ff824103489072e
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/config_parser.cpp b/src/config_parser.cpp
index 599908e..1e8e646 100644
--- a/src/config_parser.cpp
+++ b/src/config_parser.cpp
@@ -82,7 +82,7 @@
                      [](const Value& v) { return std::string(v); });
 }
 
-void KeyCheck::operator()(const std::string& s)
+void KeyCheck::operator()(std::string_view s)
 {
     for (auto c : s)
     {
@@ -94,7 +94,7 @@
     }
 }
 
-void SectionCheck::operator()(const std::string& s)
+void SectionCheck::operator()(std::string_view s)
 {
     for (auto c : s)
     {
@@ -106,7 +106,7 @@
     }
 }
 
-void ValueCheck::operator()(const std::string& s)
+void ValueCheck::operator()(std::string_view s)
 {
     for (auto c : s)
     {