Reland of: cc: Add occlusion checker as a fixed view of occlusion tracker.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index cb6aab3bace16c24d5ccc83ba1a4f16ef54e87d2..8cc9eea2dbc1804b774a9b4e141f1d9df891aca4 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -504,13 +504,14 @@ void PictureLayerImpl::UpdateTilePriorities(
   WhichTree tree =
       layer_tree_impl()->IsActiveTree() ? ACTIVE_TREE : PENDING_TREE;
   for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
-    tilings_->tiling_at(i)->UpdateTilePriorities(tree,
-                                                 visible_layer_rect,
-                                                 ideal_contents_scale_,
-                                                 current_frame_time_in_seconds,
-                                                 occlusion_tracker,
-                                                 render_target(),
-                                                 draw_transform());
+    tilings_->tiling_at(i)->UpdateTilePriorities(
+        tree,
+        visible_layer_rect,
+        ideal_contents_scale_,
+        current_frame_time_in_seconds,
+        occlusion_tracker
+            ? occlusion_tracker->GenerateOcclusionChecker(draw_transform())
+            : OcclusionChecker<LayerImpl>());
   }
 
   // Tile priorities were modified.