ozone: Fix GN build for ozone_egl_demo, ozone_unittests

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/ui.gni")
+declare_args() {
+  # Select platforms automatically. Turn this off for manual control.
+  ozone_auto_platforms = true
+}
 
-if (use_ozone) {
-  # Enable built-in ozone platforms if ozone is enabled.
-  ozone_platform_caca = false
-  ozone_platform_dri = true
-  ozone_platform_ozonex = false
-  ozone_platform_test = true
-} else {
+declare_args() {
+  # The platform that will be active by default.
+  ozone_platform = ""
+
+  # Enable individual platforms.
   ozone_platform_caca = false
   ozone_platform_dri = false
-  ozone_platform_ozonex = false
+  ozone_platform_egltest = false
+  ozone_platform_gbm = 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_dri = true
+    ozone_platform_test = true
+    ozone_platform_egltest = true
+  }
 }