Add is_chromecast to GN build.

ui/ozone/ozone.gni

 # 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.
 
+import("//build/config/chromecast_build.gni")
+
 declare_args() {
   # Select platforms automatically. Turn this off for manual control.
-  ozone_auto_platforms = true
+  ozone_auto_platforms = !is_chromecast
 }
 
 declare_args() {
   # The platform that will be active by default.
   ozone_platform = ""
 
   # Enable individual platforms.
   ozone_platform_caca = false
+  ozone_platform_cast = false
   ozone_platform_egltest = false
   ozone_platform_gbm = false
   ozone_platform_ozonex = false
   ozone_platform_test = false
 
   if (ozone_auto_platforms) {
     # Use test as the default platform.
     ozone_platform = "test"
 
     # Build all platforms whose deps are in install-build-deps.sh.
     # Only these platforms will be compile tested by buildbots.
     ozone_platform_gbm = true
     ozone_platform_test = true
     ozone_platform_egltest = true
+  } else if (is_chromecast) {
+    # The default platform used at runtime is "cast".
+    ozone_platform = "cast"
+
+    # This platform is the default for all Chromecast builds.
+    ozone_platform_cast = true
+
+    # For desktop Chromecast builds, override the default "cast" platform with
+    # --ozone_platform=egltest
+    ozone_platform_egltest = true
+    ozone_platform_ozonex = true

[gunsch, 2015/09/16 04:41:48]

we also use ozone_platform_test (for our automated test running)

[slan, 2015/09/16 16:13:08]

Added.

   }
 }