Switch DRM platform to using a separate thread

ui/ozone/platform/drm/gpu/gbm_buffer.cc

Index: ui/ozone/platform/drm/gpu/gbm_buffer.cc
diff --git a/ui/ozone/platform/drm/gpu/gbm_buffer.cc b/ui/ozone/platform/drm/gpu/gbm_buffer.cc
index 3d07983a8ee5baaa4e9269684efd229b5cc01eeb..b974f8a045573cea26fba22f8bfb49f57bd36a0c 100644
--- a/ui/ozone/platform/drm/gpu/gbm_buffer.cc
+++ b/ui/ozone/platform/drm/gpu/gbm_buffer.cc
@@ -14,8 +14,10 @@
 #include "base/trace_event/trace_event.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/native_pixmap_handle_ozone.h"
-#include "ui/ozone/platform/drm/gpu/drm_window.h"
+#include "ui/ozone/platform/drm/gpu/drm_thread.h"
+#include "ui/ozone/platform/drm/gpu/drm_window_proxy.h"
 #include "ui/ozone/platform/drm/gpu/gbm_device.h"
+#include "ui/ozone/platform/drm/gpu/proxy_helpers.h"
 
 namespace ui {
 
@@ -72,9 +74,8 @@ scoped_refptr<GbmBuffer> GbmBuffer::CreateBuffer(
 }
 
 GbmPixmap::GbmPixmap(const scoped_refptr<GbmBuffer>& buffer,
-                     ScreenManager* screen_manager)
-    : buffer_(buffer), screen_manager_(screen_manager) {
-}
+                     DrmThread* drm_thread)
+    : buffer_(buffer), drm_thread_(drm_thread) {}
 
 bool GbmPixmap::Initialize() {
   // We want to use the GBM API because it's going to call into libdrm
@@ -145,7 +146,10 @@ bool GbmPixmap::ScheduleOverlayPlane(gfx::AcceleratedWidget widget,
     }
   }
 
-  screen_manager_->GetWindow(widget)->QueueOverlayPlane(OverlayPlane(
+  if (!cached_window_ || cached_window_->widget() != widget)
+    cached_window_ = drm_thread_->CreateWindowProxy(widget);
+
+  cached_window_->QueueOverlayPlane(OverlayPlane(
       buffer_, plane_z_order, plane_transform, display_bounds, crop_rect));
   return true;
 }