Prevent overlay scrollbars expand or hover together

cc/BUILD.gn

Index: cc/BUILD.gn
diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index d16ec63ba57d8b8cbf0173c754313734f8f878ff..bad1237da31c0f7a64dd8b1ae728b75369a0c488 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn
@@ -90,11 +90,14 @@ cc_component("cc") {
     "input/scroll_state_data.h",
     "input/scrollbar_animation_controller.cc",
     "input/scrollbar_animation_controller.h",
+    "input/scrollbar_animation_controller_client.h",
     "input/scrollbar_animation_controller_linear_fade.cc",
     "input/scrollbar_animation_controller_linear_fade.h",
     "input/scrollbar_animation_controller_thinning.cc",
     "input/scrollbar_animation_controller_thinning.h",
     "input/selection.h",
+    "input/single_scrollbar_animation_controller_thinning.cc",
+    "input/single_scrollbar_animation_controller_thinning.h",
     "layers/append_quads_data.h",
     "layers/content_layer_client.h",
     "layers/draw_properties.cc",
@@ -810,6 +813,7 @@ cc_test("cc_unittests") {
     "input/scroll_state_unittest.cc",
     "input/scrollbar_animation_controller_linear_fade_unittest.cc",
     "input/scrollbar_animation_controller_thinning_unittest.cc",
+    "input/single_scrollbar_animation_controller_thinning_unittest.cc",
     "ipc/cc_param_traits_unittest.cc",
     "ipc/struct_traits_unittest.cc",
     "layers/heads_up_display_layer_impl_unittest.cc",