Overscroll and Elasticity for views::ScrollView

ui/compositor/overscroll/ui_input_handler.cc

Index: ui/compositor/overscroll/ui_input_handler.cc
diff --git a/ui/compositor/overscroll/ui_input_handler.cc b/ui/compositor/overscroll/ui_input_handler.cc
index 76e7e9018573f3410d70435c64eafbe698f46f9f..2564a639370742674401de9bc5866d0866294160 100644
--- a/ui/compositor/overscroll/ui_input_handler.cc
+++ b/ui/compositor/overscroll/ui_input_handler.cc
@@ -46,11 +46,15 @@ void UIInputHandler::WillShutdown() {
   input_handler_ = nullptr;
 }
 
-void UIInputHandler::Animate(base::TimeTicks time) {}
+void UIInputHandler::Animate(base::TimeTicks time) {
+  scroll_elasticity_controller_.Animate(time);
+}
 
 void UIInputHandler::MainThreadHasStoppedFlinging() {}
 
-void UIInputHandler::ReconcileElasticOverscrollAndRootScroll() {}
+void UIInputHandler::ReconcileElasticOverscrollAndRootScroll() {
+  scroll_elasticity_controller_.ReconcileStretchAndScroll();
+}
 
 void UIInputHandler::UpdateRootLayerStateForSynchronousInputHandler(
     const gfx::ScrollOffset& total_scroll_offset,
@@ -64,12 +68,30 @@ void UIInputHandler::HandleScrollUpdate(const ScrollEvent& scroll,
                                         cc::ElementId element) {
   cc::ScrollState scroll_state = CreateScrollState(scroll, false);
   scroll_state.data()->set_current_native_scrolling_element(element);
-  input_handler_->ScrollBy(&scroll_state);
+  cc::InputHandlerScrollResult result = input_handler_->ScrollBy(&scroll_state);
+
+  base::WeakPtr<cc::ScrollElasticityHelper> overscroll_helper =
+      input_handler_->ScrollElasticityHelperForScrollingLayer();
+  if (!overscroll_helper)
+    return;  // E.g., the scrolling layer doesn't support overscroll.
+
+  scroll_elasticity_controller_.SetActiveHelper(overscroll_helper);
+
+  gfx::Vector2dF event_delta(scroll_state.delta_x(), scroll_state.delta_y());
+  bool begin = scroll.momentum_phase() == EventMomentumPhase::MAY_BEGIN;
+  bool momentum_begin = event_delta.IsZero() &&
+      scroll.momentum_phase() == EventMomentumPhase::INERTIAL_UPDATE;
+
+  scroll_elasticity_controller_.ObserveRealScrollBegin(momentum_begin, begin);
+  scroll_elasticity_controller_.ObserveScrollUpdate(
+      event_delta, result.unused_scroll_delta, scroll.time_stamp(),
+      scroll_state.is_in_inertial_phase());
 }
 
 void UIInputHandler::HandleScrollEnd(const ScrollEvent& scroll) {
   cc::ScrollState scroll_state = CreateScrollState(scroll, true);
   input_handler_->ScrollEnd(&scroll_state);
+  scroll_elasticity_controller_.ObserveRealScrollEnd(scroll.time_stamp());
 }
 
 }  // namespace ui