Route Scroll events through a cc::InputHandler

ui/views/controls/scrollbar/base_scroll_bar.cc

Index: ui/views/controls/scrollbar/base_scroll_bar.cc
diff --git a/ui/views/controls/scrollbar/base_scroll_bar.cc b/ui/views/controls/scrollbar/base_scroll_bar.cc
index 123e59c24cc2b1198778229773d44559ca8bc569..66601d12fe1a92333ce433bfbee18219002ba4f5 100644
--- a/ui/views/controls/scrollbar/base_scroll_bar.cc
+++ b/ui/views/controls/scrollbar/base_scroll_bar.cc
@@ -177,6 +177,10 @@ bool BaseScrollBar::OnMouseWheel(const ui::MouseWheelEvent& event) {
   return true;
 }
 
+void BaseScrollBar::OnScrollEvent(ui::ScrollEvent* event) {
+  controller()->OnScrollEventFromScrollBar(event);
+}
+
 void BaseScrollBar::OnGestureEvent(ui::GestureEvent* event) {
   // If a fling is in progress, then stop the fling for any incoming gesture
   // event (except for the GESTURE_END event that is generated at the end of the