Rename "test" ozone platform to "headless"

ui/ozone/platform/headless/BUILD.gn

Index: ui/ozone/platform/headless/BUILD.gn
diff --git a/ui/ozone/platform/headless/BUILD.gn b/ui/ozone/platform/headless/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..fb731a26c2ae6f9ac2fe962bcebcce27c4ba2dc1
--- /dev/null
+++ b/ui/ozone/platform/headless/BUILD.gn
@@ -0,0 +1,27 @@
+# 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.
+
+source_set("headless") {
+  sources = [
+    "client_native_pixmap_factory_headless.cc",
+    "client_native_pixmap_factory_headless.h",
+    "headless_surface_factory.cc",
+    "headless_surface_factory.h",
+    "headless_window.cc",
+    "headless_window.h",
+    "headless_window_manager.cc",
+    "headless_window_manager.h",
+    "ozone_platform_headless.cc",
+    "ozone_platform_headless.h",
+  ]
+
+  deps = [
+    "//base",
+    "//skia",
+    "//ui/base",
+    "//ui/gfx/geometry",
+    "//ui/events/ozone:events_ozone_layout",
+    "//ui/events/platform",
+  ]
+}