Changes to support Android Things N on Cast master

Test: Built and Run with Android N(on Cast Master) changes (Cast + setup) on the AT1
Bug: 118437285
Change-Id: Iff72a2a2d8eabda619940a256bab1b23daf00c26
Reviewed-on: https://chromium-review.googlesource.com/c/1331579
Commit-Queue: Elvin L <elvin@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608393}

diff --git a/chromecast/chromecast.gni b/chromecast/chromecast.gni
index da609a9..02a14ff 100644
--- a/chromecast/chromecast.gni
+++ b/chromecast/chromecast.gni

@@ -101,6 +101,9 @@
 
   # Set to true to enable wayland server
   enable_cast_wayland_server = false
+
+  # Whether to build cast for Android Things N version
+  build_for_android_things_n = false
 }
 
 declare_args() {