Disable overlay scrollbars in Blink when hidden by the compositor.

cc/input/scrollbar_animation_controller_linear_fade_unittest.cc

Index: cc/input/scrollbar_animation_controller_linear_fade_unittest.cc
diff --git a/cc/input/scrollbar_animation_controller_linear_fade_unittest.cc b/cc/input/scrollbar_animation_controller_linear_fade_unittest.cc
index 06c4aa98dfa0693dfd4be4d3a1172432dcc86bbb..cc79c3761e9b270d0e6d9a0c9d4f61b0a8869962 100644
--- a/cc/input/scrollbar_animation_controller_linear_fade_unittest.cc
+++ b/cc/input/scrollbar_animation_controller_linear_fade_unittest.cc
@@ -39,6 +39,7 @@ class ScrollbarAnimationControllerLinearFadeTest
   ScrollbarSet ScrollbarsFor(int scroll_layer_id) const override {
     return host_impl_.ScrollbarsFor(scroll_layer_id);
   }
+  void DidChangeScrollbarVisibility() override {}
 
  protected:
   void SetUp() override {