cc: Fix bug in generating picture layer pairs from 2 lists.

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 95e1ab1866834c9582ad4f95a117bbdbc44f97f2..ec302df1a267a74e3e97a20383f29a42a874e95f 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1238,9 +1238,12 @@ void LayerTreeHostImpl::GetPictureLayerImplPairs(
     for (auto& layer : pending_tree_->picture_layers()) {
       if (need_valid_tile_priorities && !layer->HasValidTilePriorities())
         continue;
-      if (layer->GetPendingOrActiveTwinLayer()) {
-        // Already captured from the active tree.
-        continue;
+      if (PictureLayerImpl* twin_layer = layer->GetPendingOrActiveTwinLayer()) {
+        if (!need_valid_tile_priorities ||
+            twin_layer->HasValidTilePriorities()) {
+          // Already captured from the active tree.
+          continue;
+        }
       }
       layer_pairs->push_back(PictureLayerImpl::Pair(nullptr, layer));
     }