Adding fading effect for paint rectangles in HUD.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index a7f251b8ee475f69afd357b43791fbde2cd29068..476c41173587457c9d831591373512a7ff5ecbcf 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -715,7 +715,9 @@ DrawSwapReadbackResult::DrawResult LayerTreeHostImpl::CalculateRenderPasses(
       !root_surface->layer_list().empty();
   if (root_surface_has_contributing_layers &&
       root_surface_has_no_visible_damage &&
-      active_tree_->LayersWithCopyOutputRequest().empty()) {
+      active_tree_->LayersWithCopyOutputRequest().empty() &&
+      (!active_tree_->hud_layer() ||
+       !active_tree_->hud_layer()->NeedsUpdate())) {
     TRACE_EVENT0("cc",
                  "LayerTreeHostImpl::CalculateRenderPasses::EmptyDamageRect");
     frame->has_no_damage = true;