Make building seccomp-bpf a GYP condition

components/nacl.gyp

Index: components/nacl.gyp
diff --git a/components/nacl.gyp b/components/nacl.gyp
index 3a86d2df4ddcdb730072aaaacadb68b9abe308cf..287cb08100f86a6cc642f2809da253e7a5fef5f4 100644
--- a/components/nacl.gyp
+++ b/components/nacl.gyp
@@ -191,9 +191,6 @@
                 'nacl/loader/nacl_helper_linux.h',
                 '../base/posix/unix_domain_socket_linux.cc',
                 '../content/common/child_process_sandbox_support_impl_shm_linux.cc',
-                '../content/common/sandbox_linux/sandbox_bpf_base_policy_linux.cc',
-                '../content/common/sandbox_linux/sandbox_init_linux.cc',
-                '../content/common/sandbox_linux/sandbox_seccomp_bpf_linux.cc',
                 '../content/public/common/content_switches.cc',
               ],
               'conditions': [
@@ -216,6 +213,19 @@
                     }],
                   ],
                 }],
+                ['use_seccomp_bpf == 1', {
+                  'sources': [
+                    '../content/common/sandbox_linux/sandbox_bpf_base_policy_linux.cc',
+                    '../content/common/sandbox_linux/sandbox_init_linux.cc',
+                    '../content/common/sandbox_linux/sandbox_seccomp_bpf_linux.cc',
+                  ],
+                  'defines': ['USE_SECCOMP_BPF'],
+                }, {
+                  'sources': [
+                    # Included in both cases

[Mark Seaborn, 2013/12/18 08:10:21]

So why not leave it in the unconditional sources list above?  (With a comment if
you want one.)

[jln (very slow on Chromium), 2013/12/19 00:00:19]

Yeah, I think I misunderstood how "defines" worked.

Done, thanks.

+                    '../content/common/sandbox_linux/sandbox_seccomp_bpf_linux.cc',
+                  ],
+                }],
               ],
               'cflags': ['-fPIE'],
               'link_settings': {