cc: Add a flag to check for tile priority inversion in AssignGpuMemory.

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 28f129a01ae2eb971efbc2c48e528c483db98892..f369343cceca7cfe28db066f5b209b005241cef6 100644
--- a/cc/trees/layer_tree_settings.h
+++ b/cc/trees/layer_tree_settings.h
@@ -103,6 +103,10 @@ class CC_EXPORT LayerTreeSettings {
   bool use_cached_picture_raster = true;
   bool enable_color_correct_rendering = false;
 
+  // If set to true, this causes TileManager to verify that all required and NOW
+  // tiles come before lower priority tiles.
+  bool check_tile_priority_inversion = false;
+
   LayerTreeDebugState initial_debug_state;
 };