Make tile size a function of the device scale factor.

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 a04ace031729e88c156ee171495e740a8d747339..429199463d237f88e43e26a85d21267e6cb5bc83 100644
--- a/cc/trees/layer_tree_settings.h
+++ b/cc/trees/layer_tree_settings.h
@@ -71,8 +71,7 @@ class CC_EXPORT LayerTreeSettings {
   float top_controls_show_threshold = 0.5f;
   float top_controls_hide_threshold = 0.5f;
   double background_animation_rate = 1.0;
-  gfx::Size default_tile_size;
-  gfx::Size max_untiled_layer_size;
+  bool use_viewport_for_tile_size = false;
   gfx::Size minimum_occlusion_tracking_size;
   // 3000 pixels should give sufficient area for prepainting.
   // Note this value is specified with an ideal contents scale in mind. That