Make building seccomp-bpf a GYP condition

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index f07719c66ec0422a1a2f47cc4d77c24b5e0dff85..ae97babb6c8c3e681c93fcce46cadf0e302be2d3 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1916,6 +1916,16 @@
           }],
         ],
       }],
+      # seccomp-bpf is only supportd on three architectures currently.

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

Typo: "supported".  Maybe say "seccomp-bpf sandbox" to provide a little more
context.

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

Done.

+      # Do not disable seccomp_bpf anywhere without talking to
+      # security@chromium.org!
+      ['((OS=="linux" or OS=="android") and '
+           '(target_arch=="ia32" or target_arch=="x64" or '
+             'target_arch=="arm"))', {
+         'use_seccomp_bpf%': 1,
+      }, {
+         'use_seccomp_bpf%': 0,
+      }]

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

Nit: add trailing comma

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

Done.

     ],
 
     # The path to the ANGLE library.