gpu: Empty swaps for surfaceless output surfaces.

services/ui/surfaces/display_output_surface_ozone.cc

Index: services/ui/surfaces/display_output_surface_ozone.cc
diff --git a/services/ui/surfaces/display_output_surface_ozone.cc b/services/ui/surfaces/display_output_surface_ozone.cc
index e63a2e88941bbe37f5c6ce8688619a5d8befa04b..da565dd3db66963c6c7731a0245aa214fa2994dc 100644
--- a/services/ui/surfaces/display_output_surface_ozone.cc
+++ b/services/ui/surfaces/display_output_surface_ozone.cc
@@ -83,8 +83,14 @@ void DisplayOutputSurfaceOzone::SwapBuffers(cc::OutputSurfaceFrame frame) {
   DCHECK(reshape_size_ == frame.size);
   swap_size_ = reshape_size_;
 
-  buffer_queue_->SwapBuffers(frame.sub_buffer_rect ? *frame.sub_buffer_rect
-                                                   : gfx::Rect(swap_size_));
+  gfx::Rect damage_rect =
+      frame.sub_buffer_rect ? *frame.sub_buffer_rect : gfx::Rect(swap_size_);
+  // Use previous buffer when damage rect is empty. This avoids unnecessary
+  // partial swap work and makes it possible to support empty swaps on devices
+  // where partial swaps are disabled.
+  if (!damage_rect.IsEmpty())
+    buffer_queue_->SwapBuffers(damage_rect);
+
   DisplayOutputSurface::SwapBuffers(std::move(frame));
 }
 
@@ -98,7 +104,7 @@ bool DisplayOutputSurfaceOzone::IsDisplayedAsOverlayPlane() const {
 }
 
 unsigned DisplayOutputSurfaceOzone::GetOverlayTextureId() const {
-  return buffer_queue_->current_texture_id();
+  return buffer_queue_->GetCurrentTextureId();
 }
 
 void DisplayOutputSurfaceOzone::DidReceiveSwapBuffersAck(