Demo: Build NamespaceSandbox::ForkInNewPidNamespace.

sandbox/linux/services/namespace_sandbox.cc

Index: sandbox/linux/services/namespace_sandbox.cc
diff --git a/sandbox/linux/services/namespace_sandbox.cc b/sandbox/linux/services/namespace_sandbox.cc
index 23796446f3044e88a6ddcb5d6e38fb41156e8456..ce8ecf1c0d2e71e42293e297ba116ead48ab6ed2 100644
--- a/sandbox/linux/services/namespace_sandbox.cc
+++ b/sandbox/linux/services/namespace_sandbox.cc
@@ -24,6 +24,7 @@
 #include "base/process/process.h"
 #include "sandbox/linux/services/credentials.h"
 #include "sandbox/linux/services/namespace_utils.h"
+#include "sandbox/linux/system_headers/linux_signal.h"
 
 namespace sandbox {
 
@@ -131,26 +132,6 @@ base::Process NamespaceSandbox::LaunchProcess(
 }
 
 // static
-pid_t NamespaceSandbox::ForkInNewPidNamespace(bool drop_capabilities_in_child) {
-  const pid_t pid =
-      base::ForkWithFlags(CLONE_NEWPID | SIGCHLD, nullptr, nullptr);
-  if (pid < 0) {
-    return pid;
-  }
-
-  if (pid == 0) {
-    DCHECK_EQ(1, getpid());
-    if (drop_capabilities_in_child) {
-      // Since we just forked, we are single-threaded, so this should be safe.
-      CHECK(Credentials::DropAllCapabilitiesOnCurrentThread());
-    }
-    return 0;
-  }
-
-  return pid;
-}
-
-// static
 void NamespaceSandbox::InstallDefaultTerminationSignalHandlers() {
   static const int kDefaultTermSignals[] = {
       SIGHUP, SIGINT, SIGABRT, SIGQUIT, SIGPIPE, SIGTERM, SIGUSR1, SIGUSR2,
@@ -191,6 +172,26 @@ bool NamespaceSandbox::InstallTerminationSignalHandler(
 #endif  // !defined(OS_NACL_NONSFI)
 
 // static
+pid_t NamespaceSandbox::ForkInNewPidNamespace(bool drop_capabilities_in_child) {
+  const pid_t pid =
+      base::ForkWithFlags(CLONE_NEWPID | LINUX_SIGCHLD, nullptr, nullptr);
+  if (pid < 0) {
+    return pid;
+  }
+
+  if (pid == 0) {
+    DCHECK_EQ(1, getpid());
+    if (drop_capabilities_in_child) {
+      // Since we just forked, we are single-threaded, so this should be safe.
+      CHECK(Credentials::DropAllCapabilitiesOnCurrentThread());
+    }
+    return 0;
+  }
+
+  return pid;
+}
+
+// static
 bool NamespaceSandbox::InNewUserNamespace() {
   return getenv(kSandboxUSERNSEnvironmentVarName) != nullptr;
 }