Extract hardcoded error strings into a single place and replace them with enum.

src/x64/regexp-macro-assembler-x64.cc

Index: src/x64/regexp-macro-assembler-x64.cc
diff --git a/src/x64/regexp-macro-assembler-x64.cc b/src/x64/regexp-macro-assembler-x64.cc
index 106ffb76da58fbdfab942a8442672199f0115bcd..dcd317c666edbd122e65de85c392d076aa1329ce 100644
--- a/src/x64/regexp-macro-assembler-x64.cc
+++ b/src/x64/regexp-macro-assembler-x64.cc
@@ -397,7 +397,7 @@ void RegExpMacroAssemblerX64::CheckNotBackReference(
   // Fail on partial or illegal capture (start of capture after end of capture).
   // This must not happen (no back-reference can reference a capture that wasn't
   // closed before in the reg-exp).
-  __ Check(greater_equal, "Invalid capture referenced");
+  __ Check(greater_equal, kInvalidCaptureReferenced);
 
   // Succeed on empty capture (including non-participating capture)
   __ j(equal, &fallthrough);