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

test/cctest/test-code-stubs-ia32.cc

Index: test/cctest/test-code-stubs-ia32.cc
diff --git a/test/cctest/test-code-stubs-ia32.cc b/test/cctest/test-code-stubs-ia32.cc
index 6f8de604715ad9a84dbadac6508c4c88c1ccda6c..a3c0b54e259e9c1f5547a051937e7858725c3283 100644
--- a/test/cctest/test-code-stubs-ia32.cc
+++ b/test/cctest/test-code-stubs-ia32.cc
@@ -94,7 +94,7 @@ ConvertDToIFunc MakeConvertDToIFuncTrampoline(Isolate* isolate,
     Register reg = Register::from_code(reg_num);
     if (!reg.is(esp) && !reg.is(ebp) && !reg.is(destination_reg)) {
       __ cmp(reg, MemOperand(esp, 0));
-      __ Assert(equal, "register was clobbered");
+      __ Assert(equal, kRegisterWasClobbered);
       __ add(esp, Immediate(kPointerSize));
     }
   }