aura: Add missing test file to ozone GN build

It is already in the GYP build.

BUG=445627
TEST=gn gen out_gn_ozone --args='os="chromeos" use_ozone=true is_component_build=true' &&
  ninja -C out_gn_ozone chrome ozone_unittests (along with other needed changes)

Review URL: https://codereview.chromium.org/899723003

Cr-Commit-Position: refs/heads/master@{#314595}

ui/aura/BUILD.gn

@@ -206,6 +206,10 @@ source_set("test_support") {
 
     deps += [ "//ui/gfx/x" ]
   }
+
+  if (use_ozone) {
+    sources += [ "test/ui_controls_factory_ozone.cc" ]
+  }
 }
 
 executable("demo") {