Stub out ScreenManagerOzoneExternal

services/ui/display/BUILD.gn

Index: services/ui/display/BUILD.gn
diff --git a/services/ui/display/BUILD.gn b/services/ui/display/BUILD.gn
index c0bd6e7338f1dfab053ea4e977733a309063b965..ddd6894adf36afe8765916e7846985efa344a0e9 100644
--- a/services/ui/display/BUILD.gn
+++ b/services/ui/display/BUILD.gn
@@ -21,19 +21,26 @@ source_set("display") {
     "//ui/gfx",
   ]
 
-  if (use_ozone && is_chromeos) {
-    sources += [
-      "screen_manager_ozone_internal.cc",
-      "screen_manager_ozone_internal.h",
-    ]
+  if (use_ozone) {
+    if (is_chromeos) {
+      sources += [
+        "screen_manager_ozone_internal.cc",
+        "screen_manager_ozone_internal.h",
+      ]
 
-    deps += [
-      "//chromeos",
-      "//services/ui/public/interfaces/display",
-      "//skia",
-      "//ui/display/manager",
-      "//ui/ozone",
-    ]
+      deps += [
+        "//chromeos",
+        "//services/ui/public/interfaces/display",
+        "//skia",
+        "//ui/display/manager",
+        "//ui/ozone",
+      ]
+    } else {
+      sources += [
+        "screen_manager_ozone_external.cc",
+        "screen_manager_ozone_external.h",
+      ]
+    }
   } else {
     sources += [
       "screen_manager_stub_internal.cc",