cc: Add flag to disable future mask tiling.

cc/trees/layer_tree_settings.h

Index: cc/trees/layer_tree_settings.h
diff --git a/cc/trees/layer_tree_settings.h b/cc/trees/layer_tree_settings.h
index 9aecae6ee69395b18c7066c0867b4256a138c628..107a5a4d5e054e7ebf038bdb068251a18d8ca1f6 100644
--- a/cc/trees/layer_tree_settings.h
+++ b/cc/trees/layer_tree_settings.h
@@ -95,6 +95,10 @@ class CC_EXPORT LayerTreeSettings {
   // tiles come before lower priority tiles.
   bool check_tile_priority_inversion = false;
 
+  // TODO(sunxd): remove this flag when filter demoting and aa of mask layers
+  // are implemented.
+  bool enable_mask_tiling = false;
+
   LayerTreeDebugState initial_debug_state;
 };