GN: Get os="chromeos" use_ozone=true to compile

ui/ozone/gpu/BUILD.gn

Index: ui/ozone/gpu/BUILD.gn
diff --git a/ui/ozone/demo/BUILD.gn b/ui/ozone/gpu/BUILD.gn
similarity index 57%
copy from ui/ozone/demo/BUILD.gn
copy to ui/ozone/gpu/BUILD.gn
index c58431bf9191cb53a4703a94899259a222ab14d3..91d38f9c2b098c6dc7b97b2333243246624d2ecf 100644
--- a/ui/ozone/demo/BUILD.gn
+++ b/ui/ozone/gpu/BUILD.gn
@@ -2,22 +2,18 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-group("demo") {
-  deps = [
-    ":ozone_demo",
-  ]
-}
-
-executable("ozone_demo") {
+component("gpu") {
   sources = [
-    "ozone_demo.cc",
+    "gpu_memory_buffer_factory_ozone_native_buffer.cc",
+    "gpu_memory_buffer_factory_ozone_native_buffer.h",
   ]
 
+  defines = [ "OZONE_GPU_IMPLEMENTATION" ]
+
   deps = [
     "//base",
-    "//skia",
+    "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/gl",
-    "//ui/ozone",
   ]
 }