Move a couple of utility functions to a new namespace_utils class.

sandbox/linux/BUILD.gn

Index: sandbox/linux/BUILD.gn
diff --git a/sandbox/linux/BUILD.gn b/sandbox/linux/BUILD.gn
index af3a95063997a2d9962978df5a17b444725c1eb0..c9396bdb7b0f2a57ad4f9cb3c9226857b5278619 100644
--- a/sandbox/linux/BUILD.gn
+++ b/sandbox/linux/BUILD.gn
@@ -113,6 +113,7 @@ test("sandbox_linux_unittests") {
   if (compile_credentials) {
     sources += [
       "services/credentials_unittest.cc",
+      "services/namespace_utils_unittest.cc",
       "services/proc_util_unittest.cc",
       "services/unix_domain_socket_unittest.cc",
     ]
@@ -252,6 +253,8 @@ component("sandbox_services") {
     sources += [
       "services/credentials.cc",
       "services/credentials.h",
+      "services/namespace_utils.cc",
+      "services/namespace_utils.h",
       "services/proc_util.cc",
       "services/proc_util.h",
     ]