Do not use overlays when VR shell is enabled.

ui/display/display.h

Index: ui/display/display.h
diff --git a/ui/display/display.h b/ui/display/display.h
index b9d48b6c7ed74d16b9665a5f6a92e865e920e6a1..66d5d5b753468307fd3046e94b710b89f1faf43a 100644
--- a/ui/display/display.h
+++ b/ui/display/display.h
@@ -191,6 +191,13 @@ class DISPLAY_EXPORT Display final {
     is_monochrome_ = is_monochrome;
   }
 
+  // True if this is a virtual display (e.g, for vr).
+  bool in_vr() const { return true; }
+  void set_in_vr(bool in_vr) {
+    in_vr_ = in_vr;
+  }
+
+
  private:
   int64_t id_;
   gfx::Rect bounds_;
@@ -203,6 +210,7 @@ class DISPLAY_EXPORT Display final {
   int color_depth_;
   int depth_per_component_;
   bool is_monochrome_;
+  bool in_vr_;
 
 #if !defined(OS_IOS)
   friend struct mojo::StructTraits<display::mojom::DisplayDataView,