Add GN build for Linux sandbox.

sandbox/BUILD.gn

Index: sandbox/BUILD.gn
diff --git a/sandbox/BUILD.gn b/sandbox/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..ffe22a457d38bd6ba9ded891e4c936c0243cfb10
--- /dev/null
+++ b/sandbox/BUILD.gn
@@ -0,0 +1,15 @@
+# Copyright 2014 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.
+
+# Meta-target that forwards to the proper platform one.
+group("sandbox") {
+  if (is_win) {
+    deps = [ "//sandbox/win:sandbox" ]
+  # TODO(GYP)
+  #} else if (is_mac) {
+  #  deps = [ "//sandbox/mac:sandbox" ]
+  #} else if (is_linux || is_android) {
+  #  deps = [ "//sandbox/linux:sandbox" ]
+  }
+}