[NaCl SDK] Fix url_loader example for MSVC 2013

This is the same issue as in 8d01729a. MSVC 2013 now requires including
<algorithm> to use std::{min, max}.

BUG=none
R=sbc@chromium.org

Review URL: https://codereview.chromium.org/607923002

Cr-Commit-Position: refs/heads/master@{#296984}

native_client_sdk/src/examples/api/url_loader/url_loader_handler.cc

@@ -4,6 +4,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <algorithm>
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/ppb_instance.h"
 #include "ppapi/cpp/module.h"