Hide pinch viewport scrollbars when near minimum scale.

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 f1bde3272295d62afc259994115c3806a987abb9..9c0e9a348cbf00be1b4a1b4b885f581ed8738595 100644
--- a/cc/trees/layer_tree_settings.h
+++ b/cc/trees/layer_tree_settings.h
@@ -46,6 +46,7 @@ class CC_EXPORT LayerTreeSettings {
   int scrollbar_fade_delay_ms;
   int scrollbar_fade_resize_delay_ms;
   int scrollbar_fade_duration_ms;
+  float scrollbar_show_scale_threshold;
   SkColor solid_color_scrollbar_color;
   bool calculate_top_controls_position;
   bool timeout_and_draw_when_animation_checkerboards;