Revert of Overlays: Remove special casing of primary overlay plane

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index 536ab50082dc29dac38c6ee84ebff9dc40abe056..11a4b450a14d98648d64bb4345e0bdcf9eb8d061 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -3515,6 +3515,10 @@
   ResourceProvider::ResourceIdArray resources;
   OverlayCandidateList& overlays = frame->overlay_list;
   for (const OverlayCandidate& overlay : overlays) {
+    // Skip primary plane.
+    if (overlay.plane_z_order == 0)
+      continue;
+
     unsigned texture_id = 0;
     if (overlay.use_output_surface_for_resource) {
       texture_id = output_surface_->GetOverlayTextureId();