Apply clang-tidy's performance-unnecessary-value-param to clang-tidy.

No functionality change intended.

llvm-svn: 298442
diff --git a/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp b/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp
index c1c2eb7..328ddf7 100644
--- a/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp
@@ -49,7 +49,7 @@
     return Val.first.getRawEncoding() + SecondHash(Val.second);
   }
 
-  static bool isEqual(NamingCheckId LHS, NamingCheckId RHS) {
+  static bool isEqual(const NamingCheckId &LHS, const NamingCheckId &RHS) {
     if (RHS == getEmptyKey())
       return LHS == getEmptyKey();
     if (RHS == getTombstoneKey())