Preliminary compositor disabling patch.

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 32c1db514e2e1b110c271b3afdb313ebb834a045..59c733ec682b764554bdf6100a329e08295a0c0e 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -690,14 +690,16 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
   // frame at all.
   RenderSurfaceImpl* root_surface =
       active_tree_->root_layer()->render_surface();
+  gfx::Rect damage_rect_with_overlays =
+      gfx::UnionRects(root_surface->damage_tracker()->current_damage_rect(),
+                      root_surface->damage_tracker()->current_overlay_rect());
   bool root_surface_has_no_visible_damage =
-      !root_surface->damage_tracker()->current_damage_rect().Intersects(
-          root_surface->content_rect());
-  bool root_surface_has_contributing_layers =
+      !damage_rect_with_overlays.Intersects(root_surface->content_rect());
+  bool root_surface_has_no_contributing_layers =
       !root_surface->layer_list().empty();
   bool hud_wants_to_draw_ = active_tree_->hud_layer() &&
                             active_tree_->hud_layer()->IsAnimatingHUDContents();
-  if (root_surface_has_contributing_layers &&
+  if (root_surface_has_no_contributing_layers &&
       root_surface_has_no_visible_damage &&
       active_tree_->LayersWithCopyOutputRequest().empty() &&
       !output_surface_->capabilities().can_force_reclaim_resources &&
@@ -899,6 +901,15 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
   }
 
   RemoveRenderPasses(CullRenderPassesWithNoQuads(), frame);
+
+  // Only the root render pass is allowed to have overlays, so we can merge
+  // in all quad damage for the other ones now.
+  for (size_t i = 0; i < frame->render_passes.size() - 1; ++i) {
+    RenderPass* pass = frame->render_passes.at(i);
+    pass->damage_rect.Union(pass->overlay_rect);
+    pass->overlay_rect = gfx::Rect();
+  }
+
   renderer_->DecideRenderPassAllocationsForFrame(frame->render_passes);
 
   // Any copy requests left in the tree are not going to get serviced, and