Aviod double checking IS_STRING when joining arrays.

Review URL: http://codereview.chromium.org/5977013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6226 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/array.js

@@ -121,6 +121,7 @@ function Join(array, length, separator, convert) {
         if (IS_STRING(e)) return e;
         return convert(e);
       }
+      return '';
     }
 
     // Construct an array for the elements.
@@ -160,7 +161,7 @@ function Join(array, length, separator, convert) {
 
 
 function ConvertToString(x) {
-  if (IS_STRING(x)) return x;
+  // Assumes x is a non-string. 
   if (IS_NUMBER(x)) return %_NumberToString(x);
   if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
   return (IS_NULL_OR_UNDEFINED(x)) ? '' : %ToString(%DefaultString(x));

src/v8natives.js

@@ -1183,7 +1183,7 @@ function NewFunction(arg1) {  // length == 1
   if (n > 1) {
     p = new $Array(n - 1);
     for (var i = 0; i < n - 1; i++) p[i] = %_Arguments(i);
-    p = Join(p, n - 1, ',', ToString);
+    p = Join(p, n - 1, ',', NonStringToString);
     // If the formal parameters string include ) - an illegal
     // character - it may make the combined function expression
     // compile. We avoid this problem by checking for this early on.