Default to enabling the namespace sandbox when possible.

content/browser/zygote_host/zygote_host_impl_linux.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/zygote_host/zygote_host_impl_linux.h"
 
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ skipping 567 matching lines @@
   return 0;
 }
 
 bool ZygoteHostImpl::ShouldUseNamespaceSandbox() {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
   if (command_line.HasSwitch(switches::kNoSandbox)) {
     return false;
   }
 
-  if (!command_line.HasSwitch(switches::kEnableNamespaceSandbox)) {
+  if (command_line.HasSwitch(switches::kDisableNamespaceSandbox)) {
     return false;
   }
 
   if (!sandbox::Credentials::CanCreateProcessInNewUserNS()) {
     return false;
   }
 
   return true;
 }
 
 }  // namespace content