Pass root ServerWindow id to FrameGenerator.

services/ui/ws/platform_display_init_params.h

Index: services/ui/ws/platform_display_init_params.h
diff --git a/services/ui/ws/platform_display_init_params.h b/services/ui/ws/platform_display_init_params.h
index b5b049225e11cdcfcaa07434e7490a56a8db529e..9397cff7412cb7e0c6e50092fa4762dbb3d578f7 100644
--- a/services/ui/ws/platform_display_init_params.h
+++ b/services/ui/ws/platform_display_init_params.h
@@ -13,17 +13,20 @@
 namespace ui {
 
 class DisplayCompositor;
-class GpuState;
 
 namespace ws {
 
+class ServerWindow;
+
 struct PlatformDisplayInitParams {
   PlatformDisplayInitParams();
+  PlatformDisplayInitParams(const PlatformDisplayInitParams& other);
   ~PlatformDisplayInitParams();
 
   scoped_refptr<DisplayCompositor> display_compositor;
 
   int64_t display_id;
+  ServerWindow* root_window = nullptr;
   display::ViewportMetrics metrics;
 };