Revert "Fix sending scrollend on main thread snap"

This reverts commit 0d6bba53.

Reason for revert: Broke webkit_layout_tests on WebKit Linux Leak bot:

https://ci.chromium.org/p/chromium/builders/ci/WebKit%20Linux%20Leak/2935

Original change's description:
> Fix sending scrollend on main thread snap
> 
> This CL sends scrollend event if GSE is being
> handled on the main thread after the snap (if
> the snap has started after GSE). It also takes
> care of sending scrollend event for snap after
> fling.
> 
> Bug: 907601
> Change-Id: I21aba5d098b25ddc765d78a7792ec8a2fb7987cb
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1743253
> Reviewed-by: David Bokan <bokan@chromium.org>
> Commit-Queue: Navid Zolghadr <nzolghadr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#685217}

TBR=bokan@chromium.org,nzolghadr@chromium.org

Change-Id: Ib7901d4284565f8cd636e1e4064163750bf08d4e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 907601
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1744517Reviewed-by: Scott Little <sclittle@chromium.org>
Commit-Queue: Scott Little <sclittle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685254}

third_party/blink/renderer/core/input/event_handler.cc

@@ -1532,6 +1532,13 @@ WebInputEventResult EventHandler::HandleGestureScrollEvent(
   return scroll_manager_->HandleGestureScrollEvent(gesture_event);
 }
 
+WebInputEventResult EventHandler::HandleGestureScrollEnd(
+    const WebGestureEvent& gesture_event) {
+  if (!frame_->GetPage())
+    return WebInputEventResult::kNotHandled;
+  return scroll_manager_->HandleGestureScrollEnd(gesture_event);
+}
+
 void EventHandler::SetMouseDownMayStartAutoscroll() {
   mouse_event_manager_->SetMouseDownMayStartAutoscroll();
 }

third_party/blink/renderer/core/input/event_handler.h

@@ -201,6 +201,7 @@ class CORE_EXPORT EventHandler final
   // Handle the provided scroll gesture event, propagating down to child frames
   // as necessary.
   WebInputEventResult HandleGestureScrollEvent(const WebGestureEvent&);
+  WebInputEventResult HandleGestureScrollEnd(const WebGestureEvent&);
   bool IsScrollbarHandlingGestures() const;
 
   bool BestClickableNodeForHitTestResult(const HitTestLocation& location,

third_party/blink/renderer/core/input/scroll_manager.cc

@@ -113,15 +113,6 @@ void ScrollManager::ClearGestureScrollState() {
   }
 }
 
-Node* ScrollManager::GetScrollEventTarget() {
-  // Send the overscroll event to the node that scrolling is latched to which
-  // is either previously scrolled node or the last node in the scroll chain.
-  Node* scroll_target = previous_gesture_scrolled_node_;
-  if (!scroll_target && !current_scroll_chain_.IsEmpty())
-    scroll_target = DOMNodeIds::NodeForId(current_scroll_chain_.front());
-  return scroll_target;
-}
-
 void ScrollManager::StopAutoscroll() {
   if (AutoscrollController* controller = GetAutoscrollController())
     controller->StopAutoscroll();
@@ -326,12 +317,11 @@ bool ScrollManager::LogicalScroll(ScrollDirection direction,
     }
 
     ScrollableArea::ScrollCallback callback;
-    if (RuntimeEnabledFeatures::UpdateHoverAtBeginFrameEnabled() ||
-        RuntimeEnabledFeatures::OverscrollCustomizationEnabled()) {
+    if (RuntimeEnabledFeatures::UpdateHoverAtBeginFrameEnabled()) {
       callback = ScrollableArea::ScrollCallback(WTF::Bind(
           [](WeakPersistent<ScrollableArea> area) {
             if (area)
-              area->OnScrollFinished();
+              area->MarkHoverStateDirty();
           },
           WrapWeakPersistent(scrollable_area)));
     }
@@ -635,7 +625,13 @@ WebInputEventResult ScrollManager::HandleGestureScrollUpdate(
     return WebInputEventResult::kHandledSystem;
 
   if (RuntimeEnabledFeatures::OverscrollCustomizationEnabled()) {
-    if (Node* overscroll_target = GetScrollEventTarget()) {
+    // Send the overscroll event to the node that scrolling is latched to which
+    // is either previously scrolled node or the last node in the scroll chain.
+    Node* overscroll_target = previous_gesture_scrolled_node_;
+    if (!overscroll_target && !current_scroll_chain_.IsEmpty())
+      overscroll_target = DOMNodeIds::NodeForId(current_scroll_chain_.front());
+
+    if (overscroll_target) {
       overscroll_target->GetDocument().EnqueueOverscrollEventForNode(
           overscroll_target, delta.Width(), delta.Height());
     }
@@ -696,9 +692,16 @@ WebInputEventResult ScrollManager::HandleGestureScrollEnd(
     snap_at_gesture_scroll_end = SnapAtGestureScrollEnd();
     NotifyScrollPhaseEndForCustomizedScroll();
 
-    if (RuntimeEnabledFeatures::OverscrollCustomizationEnabled() &&
-        !snap_at_gesture_scroll_end) {
-      if (Node* scroll_end_target = GetScrollEventTarget()) {
+    if (RuntimeEnabledFeatures::OverscrollCustomizationEnabled()) {
+      // Send the scrollend event to the node that scrolling is latched to
+      // which is either previously scrolled node or the last node in the
+      // scroll chain.
+      DCHECK(!current_scroll_chain_.IsEmpty());
+      if (previous_gesture_scrolled_node_) {
+        previous_gesture_scrolled_node_->GetDocument()
+            .EnqueueScrollEndEventForNode(previous_gesture_scrolled_node_);
+      } else if (Node* scroll_end_target =
+                     DOMNodeIds::NodeForId(current_scroll_chain_.front())) {
         scroll_end_target->GetDocument().EnqueueScrollEndEventForNode(
             scroll_end_target);
       }
@@ -792,12 +795,6 @@ gfx::Vector2dF ScrollManager::ScrollByForSnapFling(
 }
 
 void ScrollManager::ScrollEndForSnapFling() {
-  if (RuntimeEnabledFeatures::OverscrollCustomizationEnabled()) {
-    if (Node* scroll_end_target = GetScrollEventTarget()) {
-      scroll_end_target->GetDocument().EnqueueScrollEndEventForNode(
-          scroll_end_target);
-    }
-  }
   if (current_scroll_chain_.IsEmpty()) {
     NotifyScrollPhaseEndForCustomizedScroll();
     ClearGestureScrollState();

third_party/blink/renderer/core/input/scroll_manager.h

@@ -119,8 +119,6 @@ class CORE_EXPORT ScrollManager
   WebInputEventResult PassScrollGestureEvent(const WebGestureEvent&,
                                              LayoutObject*);
 
-  Node* GetScrollEventTarget();
-
   void ClearGestureScrollState();
 
   void CustomizedScroll(ScrollState&);

third_party/blink/renderer/core/scroll/scrollable_area.cc

@@ -300,13 +300,12 @@ void ScrollableArea::ProgrammaticScrollHelper(const ScrollOffset& offset,
   CancelScrollAnimation();
 
   ScrollCallback callback = std::move(on_finish);
-  if (RuntimeEnabledFeatures::UpdateHoverAtBeginFrameEnabled() ||
-      RuntimeEnabledFeatures::OverscrollCustomizationEnabled()) {
+  if (RuntimeEnabledFeatures::UpdateHoverAtBeginFrameEnabled()) {
     callback = ScrollCallback(WTF::Bind(
         [](ScrollCallback original_callback,
            WeakPersistent<ScrollableArea> area) {
           if (area)
-            area->OnScrollFinished();
+            area->MarkHoverStateDirty();
           if (original_callback)
             std::move(original_callback).Run();
         },
@@ -818,19 +817,13 @@ CompositorElementId ScrollableArea::GetScrollbarElementId(
       scrollable_element_id.GetInternalValue(), element_id_namespace);
 }
 
-void ScrollableArea::OnScrollFinished() {
+void ScrollableArea::MarkHoverStateDirty() {
   if (GetLayoutBox()) {
-    if (RuntimeEnabledFeatures::OverscrollCustomizationEnabled()) {
-      if (Node* node = GetLayoutBox()->GetNode())
-        node->GetDocument().EnqueueScrollEndEventForNode(node);
-    }
-    if (RuntimeEnabledFeatures::UpdateHoverAtBeginFrameEnabled()) {
-      GetLayoutBox()
-          ->GetFrame()
-          ->LocalFrameRoot()
-          .GetEventHandler()
-          .MarkHoverStateDirty();
-    }
+    GetLayoutBox()
+        ->GetFrame()
+        ->LocalFrameRoot()
+        .GetEventHandler()
+        .MarkHoverStateDirty();
   }
 }
 

third_party/blink/renderer/core/scroll/scrollable_area.h

@@ -416,7 +416,7 @@ class CORE_EXPORT ScrollableArea : public GarbageCollectedMixin {
 
   virtual ScrollbarTheme& GetPageScrollbarTheme() const = 0;
 
-  void OnScrollFinished();
+  virtual void MarkHoverStateDirty();
 
   float ScrollStep(ScrollGranularity, ScrollbarOrientation) const;
 

third_party/blink/web_tests/TestExpectations

@@ -242,6 +242,11 @@ crbug.com/857490 virtual/scroll_customization/fast/events/touch/gesture/pad-gest
 crbug.com/857490 virtual/scroll_customization/fast/events/touch/gesture/touch-gesture-fling-with-page-scale.html [ Skip ]
 crbug.com/857490 virtual/scroll_customization/fast/scroll-behavior/scroll-customization/touch-scroll-customization.html [ Skip ]
 
+# Currently on main thread scrolling path, scrollend gets fired without waiting for scroll/fling snap animation. (The virtual/threaded version of the test passes.)
+crbug.com/907601 fast/scrolling/events/scrollend-event-fired-after-snap.html [ Skip ]
+crbug.com/907601 virtual/scroll_customization/fast/scrolling/events/scrollend-event-fired-after-snap.html [ Skip ]
+crbug.com/907601 external/wpt/dom/events/scrolling/scrollend-event-fired-after-snap.html [ Skip ]
+
 crbug.com/980969 [ Mac ] http/tests/input/discard-events-to-unstable-iframe.html [ Pass Failure ]
 
 # Display locking, run highlight-display-locked.js only with display locking.