Implement fade-out animation for Aura overlay scrollbars (CC only).

cc/input/scrollbar_animation_controller_linear_fade.cc

Index: cc/input/scrollbar_animation_controller_linear_fade.cc
diff --git a/cc/input/scrollbar_animation_controller_linear_fade.cc b/cc/input/scrollbar_animation_controller_linear_fade.cc
index 8695bfaf6cf57b4199e3faec1a4ae539f50a0795..ee7f4afe64827fbbf46c91fba0a111a6c925cfb8 100644
--- a/cc/input/scrollbar_animation_controller_linear_fade.cc
+++ b/cc/input/scrollbar_animation_controller_linear_fade.cc
@@ -33,8 +33,8 @@ ScrollbarAnimationControllerLinearFade::ScrollbarAnimationControllerLinearFade(
     : ScrollbarAnimationController(scroll_layer_id,
                                    client,
                                    delay_before_starting,
-                                   resize_delay_before_starting,
-                                   duration) {}
+                                   resize_delay_before_starting),
+      duration_(duration) {}
 
 ScrollbarAnimationControllerLinearFade::
     ~ScrollbarAnimationControllerLinearFade() {}
@@ -46,6 +46,10 @@ void ScrollbarAnimationControllerLinearFade::RunAnimationFrame(float progress) {
     StopAnimation();
 }
 
+const base::TimeDelta& ScrollbarAnimationControllerLinearFade::Duration() {
+  return duration_;
+}
+
 void ScrollbarAnimationControllerLinearFade::DidScrollUpdate(bool on_resize) {
   ScrollbarAnimationController::DidScrollUpdate(on_resize);
   ApplyOpacityToScrollbars(1.f);