DirectRenderer allows empty swap rects for CommitOverlayPlanes

cc/output/direct_renderer.cc

Index: cc/output/direct_renderer.cc
diff --git a/cc/output/direct_renderer.cc b/cc/output/direct_renderer.cc
index 4acd9c142ad5b3ef95638a574270d774b3d0a935..600805ad8c71cbb386c2f40de5c9e4757e197b92 100644
--- a/cc/output/direct_renderer.cc
+++ b/cc/output/direct_renderer.cc
@@ -205,9 +205,7 @@ void DirectRenderer::DrawFrame(RenderPassList* render_passes_in_draw_order,
   DrawingFrame frame;
   frame.render_passes_in_draw_order = render_passes_in_draw_order;
   frame.root_render_pass = root_render_pass;
-  frame.root_damage_rect = Capabilities().using_partial_swap
-                               ? root_render_pass->damage_rect
-                               : root_render_pass->output_rect;
+  frame.root_damage_rect = root_render_pass->damage_rect;
   frame.root_damage_rect.Union(overlay_processor_->GetAndResetOverlayDamage());
   frame.root_damage_rect.Intersect(gfx::Rect(device_viewport_rect.size()));
   frame.device_viewport_rect = device_viewport_rect;
@@ -226,8 +224,7 @@ void DirectRenderer::DrawFrame(RenderPassList* render_passes_in_draw_order,
 
   if (output_surface_->IsDisplayedAsOverlayPlane()) {
     // Create the overlay candidate for the output surface, and mark it as
-    // always
-    // handled.
+    // always handled.
     OverlayCandidate output_surface_plane;
     output_surface_plane.display_rect =
         gfx::RectF(root_render_pass->output_rect);
@@ -254,9 +251,18 @@ void DirectRenderer::DrawFrame(RenderPassList* render_passes_in_draw_order,
         &frame.ca_layer_overlay_list, &frame.root_damage_rect);
   }
 
+  // The damage rect might be empty now, but if empty swap isn't allowed we
+  // still have to draw.
+  bool should_draw = has_copy_requests || !frame.root_damage_rect.IsEmpty() ||
+                     !Capabilities().allow_empty_swap;
+  // If we have to draw but don't support partial swap the whole output should
+  // be considered damaged.
+  if (should_draw && !Capabilities().using_partial_swap)
+    frame.root_damage_rect = root_render_pass->output_rect;
+
   // If all damage is being drawn with overlays or CALayers then skip drawing
   // the render passes.
-  if (frame.root_damage_rect.IsEmpty() && !has_copy_requests) {
+  if (!should_draw) {
     BindFramebufferToOutputSurface(&frame);
   } else {
     for (const auto& pass : *render_passes_in_draw_order) {