Add is_chromecast to GN build.

build/config/ui.gni

Index: build/config/ui.gni
diff --git a/build/config/ui.gni b/build/config/ui.gni
index bf62c4d835fb2af5b6f3e2f0b0ac5ddd16fa31f5..35e8144ab2da9dd7958eedc97c83206f1102c86c 100644
--- a/build/config/ui.gni
+++ b/build/config/ui.gni
@@ -14,21 +14,25 @@
 # required. See the declare_args block of BUILDCONFIG.gn for advice on how
 # to set up feature flags.
 
+import("//build/config/chromecast_build.gni")
+
 declare_args() {
   # Indicates if Ash is enabled. Ash is the Aura Shell which provides a
   # desktop-like environment for Aura. Requires use_aura = true
-  use_ash = is_win || is_linux
+  use_ash = (is_win || is_linux) && !is_chromecast
 
   # Indicates if Ozone is enabled. Ozone is a low-level library layer for Linux
-  # that does not require X11.
-  use_ozone = false
+  # that does not require X11. Enabling this feature disables use of glib, x11,
+  # Pango, and Cairo. Default to false on non-Chromecast builds.
+  use_ozone = is_chromecast
 
   # Indicates if Aura is enabled. Aura is a low-level windowing library, sort
   # of a replacement for GDI or GTK.
-  use_aura = is_win || is_linux
+  use_aura = is_win || is_linux || is_chromecast
 
   # True means the UI is built using the "views" framework.
-  toolkit_views = is_mac || is_win || is_chromeos || use_aura
+  toolkit_views =
+      (is_mac || is_win || is_chromeos || use_aura) && !is_chromecast
 
   # Whether the entire browser uses toolkit-views on Mac instead of Cocoa.
   mac_views_browser = false