Preliminary compositor disabling patch.

cc/trees/damage_tracker.cc

Index: cc/trees/damage_tracker.cc
diff --git a/cc/trees/damage_tracker.cc b/cc/trees/damage_tracker.cc
index 235dfcfd7ef6ea316a244b31122314dfacdf2ed3..4b665541223b80f604f39496c0bc1b73e22e48da 100644
--- a/cc/trees/damage_tracker.cc
+++ b/cc/trees/damage_tracker.cc
@@ -125,8 +125,10 @@ void DamageTracker::UpdateDamageTrackingState(
   // These functions cannot be bypassed with early-exits, even if we know what
   // the damage will be for this frame, because we need to update the damage
   // tracker state to correctly track the next frame.
-  gfx::Rect damage_from_active_layers =
-      TrackDamageFromActiveLayers(layer_list, target_surface_layer_id);
+  gfx::Rect damage_from_active_layers;
+  TrackDamageFromActiveLayers(layer_list, target_surface_layer_id,
+                              &damage_from_active_layers,
+                              &current_overlay_rect_);
   gfx::Rect damage_from_surface_mask =
       TrackDamageFromSurfaceMask(target_surface_mask_layer);
   gfx::Rect damage_from_leftover_rects = TrackDamageFromLeftoverRects();
@@ -173,9 +175,10 @@ DamageTracker::RectMapData& DamageTracker::RectDataForLayer(
   return *it;
 }
 
-gfx::Rect DamageTracker::TrackDamageFromActiveLayers(
-    const LayerImplList& layer_list,
-    int target_surface_layer_id) {
+void DamageTracker::TrackDamageFromActiveLayers(const LayerImplList& layer_list,
+                                                int target_surface_layer_id,
+                                                gfx::Rect* damage,
+                                                gfx::Rect* overlay) {
   gfx::Rect damage_rect;
 
   for (size_t layer_index = 0; layer_index < layer_list.size(); ++layer_index) {
@@ -189,12 +192,10 @@ gfx::Rect DamageTracker::TrackDamageFromActiveLayers(
       continue;
     if (LayerTreeHostCommon::RenderSurfaceContributesToTarget<LayerImpl>(
             layer, target_surface_layer_id))
-      ExtendDamageForRenderSurface(layer, &damage_rect);
+      ExtendDamageForRenderSurface(layer, damage);
     else
-      ExtendDamageForLayer(layer, &damage_rect);
+      ExtendDamageForLayer(layer, damage, overlay);
   }
-
-  return damage_rect;
 }
 
 gfx::Rect DamageTracker::TrackDamageFromSurfaceMask(
@@ -260,7 +261,8 @@ gfx::Rect DamageTracker::TrackDamageFromLeftoverRects() {
 }
 
 void DamageTracker::ExtendDamageForLayer(LayerImpl* layer,
-                                         gfx::Rect* target_damage_rect) {
+                                         gfx::Rect* target_damage_rect,
+                                         gfx::Rect* target_overlay_rect) {
   // There are two ways that a layer can damage a region of the target surface:
   //   1. Property change (e.g. opacity, position, transforms):
   //        - the entire region of the layer itself damages the surface.
@@ -289,7 +291,9 @@ void DamageTracker::ExtendDamageForLayer(LayerImpl* layer,
   gfx::RectF damage_rect =
       gfx::UnionRects(layer->update_rect(), layer->damage_rect());
 
-  if (layer_is_new || layer->LayerPropertyChanged()) {
+  if (!layer->overlay_update_rect().IsEmpty()) {
+    target_overlay_rect->Union(layer->overlay_update_rect());
+  } else if (layer_is_new || layer->LayerPropertyChanged()) {
     // If a layer is new or has changed, then its entire layer rect affects the
     // target surface.
     target_damage_rect->Union(rect_in_target_space);