Bug 1200856 - Avoid the extra variable to make the string manipulation faster; r=sicking

dom/security/nsCORSListenerProxy.cpp

@@ -389,7 +389,6 @@ nsPreflightCache::GetCacheKey(nsIURI* aURI,
     port.AppendInt(NS_GetRealPort(uri));
   }
 
-  nsAutoCString cred;
   if (aWithCredentials) {
     _retval.AssignLiteral("cred");
   }
@@ -401,7 +400,7 @@ nsPreflightCache::GetCacheKey(nsIURI* aURI,
   rv = aURI->GetSpec(spec);
   NS_ENSURE_SUCCESS(rv, false);
 
-  _retval.Assign(cred + space + scheme + space + host + space + port + space +
+  _retval.Append(space + scheme + space + host + space + port + space +
                  spec);
 
   return true;