Add GN build for Linux sandbox.

build/config/linux/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/sysroot.gni")
 
 config("sdk") {
   if (sysroot != "") {
     cflags = [ "--sysroot=" + sysroot ]
@@ skipping 55 matching lines @@
 }
 
 config("xcomposite") {
   libs = [ "Xcomposite" ]
 }
 
 config("xext") {
   libs = [ "Xext" ]
 }
 
+config("libcap") {
+  libs = [ "cap" ]
+}
+
 config("libresolv") {
   libs = [ "resolv" ]
 }
 
 pkg_config("gconf") {
   packages = [ "gconf-2.0" ]
   defines = [ "USE_GCONF" ]
 }
 
 pkg_config("gio_config") {
@@ skipping 29 matching lines @@
     "g_settings_get_strv",
     "g_settings_list_schemas",
   ]
 }
 
 source_set("gio") {
   direct_dependent_configs = [ ":gio_config" ]
   sources = [ gio_output_h, gio_output_cc ]
   deps = [ ":make_gio_headers" ]
 }