cc: Don't require low res to activate for shared ready-to-draw tiles.

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 1f8e5a88aaf240695897dd27c9c31e488a225be6..763f05e1e33ccaac7a3351bf28883ace51575183 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -936,7 +936,10 @@ bool PictureLayerImpl::MarkVisibleTilesAsRequired(
     if (optional_twin_tiling) {
       Tile* twin_tile = optional_twin_tiling->TileAt(iter.i(), iter.j());
       if (!twin_tile || twin_tile == tile) {
-        twin_had_missing_tile = true;
+        // However if the shared tile is being used on the active tree, then
+        // there's no missing content in this place, and low res is not needed.
+        if (!twin_tile || !twin_tile->IsReadyToDraw())
+          twin_had_missing_tile = true;
         continue;
       }
     }