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

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

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 379 matching lines @@
   Label fallthrough;
 
   // Find length of back-referenced capture.
   __ movq(rdx, register_location(start_reg));
   __ movq(rax, register_location(start_reg + 1));
   __ subq(rax, rdx);  // Length to check.
 
   // 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);
 
   // -----------------------
   // rdx - Start of capture
   // rax - length of capture
 
   // Check that there are sufficient characters left in the input.
   __ movl(rbx, rdi);
@@ skipping 1029 matching lines @@
   }
 }
 
 #undef __
 
 #endif  // V8_INTERPRETED_REGEXP
 
 }}  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64