Convert use_seccomp_bpf to the BUILDFLAG system.

components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.cc

Index: components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.cc
diff --git a/components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.cc b/components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.cc
index 3be2e83556acb30aa7d118e4d73ccec942e6bba1..9a8d96f67fa89169369a88138722e9a13e09c8f4 100644
--- a/components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.cc
+++ b/components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.cc
@@ -9,8 +9,9 @@
 
 #include "base/macros.h"
 #include "build/build_config.h"
+#include "sandbox/sandbox_features.h"
 
-#if defined(USE_SECCOMP_BPF)
+#if BUILDFLAG(USE_SECCOMP_BPF)
 
 #include <errno.h>
 #include <signal.h>
@@ -30,11 +31,11 @@
 #include "sandbox/linux/seccomp-bpf-helpers/syscall_parameters_restrictions.h"
 #include "sandbox/linux/system_headers/linux_syscalls.h"
 
-#endif  // defined(USE_SECCOMP_BPF)
+#endif  // BUILDFLAG(USE_SECCOMP_BPF)
 
 namespace nacl {
 
-#if defined(USE_SECCOMP_BPF)
+#if BUILDFLAG(USE_SECCOMP_BPF)
 
 namespace {
 
@@ -163,10 +164,10 @@ void RunSandboxSanityChecks() {
 
 #error "Seccomp-bpf disabled on supported architecture!"
 
-#endif  // defined(USE_SECCOMP_BPF)
+#endif  // BUILDFLAG(USE_SECCOMP_BPF)
 
 bool InitializeBPFSandbox(base::ScopedFD proc_fd) {
-#if defined(USE_SECCOMP_BPF)
+#if BUILDFLAG(USE_SECCOMP_BPF)
   bool sandbox_is_initialized = content::InitializeSandbox(
       std::unique_ptr<sandbox::bpf_dsl::Policy>(new NaClBPFSandboxPolicy),
       std::move(proc_fd));
@@ -174,7 +175,7 @@ bool InitializeBPFSandbox(base::ScopedFD proc_fd) {
     RunSandboxSanityChecks();
     return true;
   }
-#endif  // defined(USE_SECCOMP_BPF)
+#endif  // BUILDFLAG(USE_SECCOMP_BPF)
   return false;
 }