vm: name anonymous functions

Name anonymous arrow function in vm module to improve readability

PR-URL: https://github.com/nodejs/node/pull/9388
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <inglor@gmail.com>
Ref: #8913

lib/vm.js

@@ -18,9 +18,10 @@ const realRunInContext = Script.prototype.runInContext;
 
 Script.prototype.runInThisContext = function(options) {
   if (options && options.breakOnSigint) {
-    return sigintHandlersWrap(() => {
+    const realRunInThisContextScript = () => {
       return realRunInThisContext.call(this, options);
-    });
+    };
+    return sigintHandlersWrap(realRunInThisContextScript);
   } else {
     return realRunInThisContext.call(this, options);
   }
@@ -28,9 +29,10 @@ Script.prototype.runInThisContext = function(options) {
 
 Script.prototype.runInContext = function(contextifiedSandbox, options) {
   if (options && options.breakOnSigint) {
-    return sigintHandlersWrap(() => {
+    const realRunInContextScript = () => {
       return realRunInContext.call(this, contextifiedSandbox, options);
-    });
+    };
+    return sigintHandlersWrap(realRunInContextScript);
   } else {
     return realRunInContext.call(this, contextifiedSandbox, options);
   }