Revert of Re-target wheel events only when a new scroll sequence has started.

third_party/WebKit/Source/core/input/MouseWheelEventManager.cpp

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/input/MouseWheelEventManager.h"
 
 #include "core/dom/Document.h"
 #include "core/events/WheelEvent.h"
 #include "core/frame/LocalFrameView.h"
 #include "core/input/EventHandler.h"
 #include "core/input/EventHandlingUtil.h"
 #include "core/input/ScrollManager.h"
 #include "core/layout/HitTestRequest.h"
 #include "core/layout/HitTestResult.h"
 #include "core/layout/api/LayoutViewItem.h"
 #include "public/platform/WebMouseWheelEvent.h"
 
 namespace blink {
 MouseWheelEventManager::MouseWheelEventManager(LocalFrame& frame,
                                                ScrollManager& scroll_manager)
-    : frame_(frame), wheel_target_(nullptr), scroll_manager_(scroll_manager) {}
+    : frame_(frame), scroll_manager_(scroll_manager) {}
 
 DEFINE_TRACE(MouseWheelEventManager) {
   visitor->Trace(frame_);
-  visitor->Trace(wheel_target_);
   visitor->Trace(scroll_manager_);
 }
 
-void MouseWheelEventManager::Clear() {
-  wheel_target_ = nullptr;
-}
-
 WebInputEventResult MouseWheelEventManager::HandleWheelEvent(
     const WebMouseWheelEvent& event) {
-  bool wheel_scroll_latching =
-      RuntimeEnabledFeatures::TouchpadAndWheelScrollLatchingEnabled();
+#if OS(MACOSX)
+  // Filter Mac OS specific phases, usually with a zero-delta.
+  // https://crbug.com/553732
+  // TODO(chongz): EventSender sends events with
+  // |WebMouseWheelEvent::PhaseNone|,
+  // but it shouldn't.
+  const int kWheelEventPhaseNoEventMask = WebMouseWheelEvent::kPhaseEnded |
+                                          WebMouseWheelEvent::kPhaseCancelled |
+                                          WebMouseWheelEvent::kPhaseMayBegin;
+  if ((event.phase & kWheelEventPhaseNoEventMask) ||
+      (event.momentum_phase & kWheelEventPhaseNoEventMask))
+    return WebInputEventResult::kNotHandled;
+#endif
+  Document* doc = frame_->GetDocument();
 
-  Document* doc = frame_->GetDocument();
-  if (!doc || doc->GetLayoutViewItem().IsNull())
+  if (doc->GetLayoutViewItem().IsNull())
     return WebInputEventResult::kNotHandled;
 
   LocalFrameView* view = frame_->View();
   if (!view)
     return WebInputEventResult::kNotHandled;
 
-  if (wheel_scroll_latching) {
-    const int kWheelEventPhaseEndedEventMask =
-        WebMouseWheelEvent::kPhaseEnded | WebMouseWheelEvent::kPhaseCancelled;
-    const int kWheelEventPhaseNoEventMask =
-        kWheelEventPhaseEndedEventMask | WebMouseWheelEvent::kPhaseMayBegin;
-
-    if ((event.phase & kWheelEventPhaseEndedEventMask) ||
-        (event.momentum_phase & kWheelEventPhaseEndedEventMask)) {
-      wheel_target_ = nullptr;
-    }
-
-    if ((event.phase & kWheelEventPhaseNoEventMask) ||
-        (event.momentum_phase & kWheelEventPhaseNoEventMask)) {
-      // Filter wheel events with zero deltas and reset the wheel_target_ node.
-      DCHECK(!event.delta_x && !event.delta_y);
-      return WebInputEventResult::kNotHandled;
-    }
-
-    if (event.phase == WebMouseWheelEvent::kPhaseBegan) {
-      // Find and save the wheel_target_, this target will be used for the rest
-      // of the current scrolling sequence.
-      DCHECK(!wheel_target_);
-      wheel_target_ = FindTargetNode(event, doc, view);
-    }
-  } else {  // !wheel_scroll_latching, wheel_target_ will be updated for each
-            // wheel event.
-#if OS(MACOSX)
-    // Filter Mac OS specific phases, usually with a zero-delta.
-    // https://crbug.com/553732
-    // TODO(chongz): EventSender sends events with
-    // |WebMouseWheelEvent::PhaseNone|,
-    // but it shouldn't.
-    const int kWheelEventPhaseNoEventMask =
-        WebMouseWheelEvent::kPhaseEnded | WebMouseWheelEvent::kPhaseCancelled |
-        WebMouseWheelEvent::kPhaseMayBegin;
-    if ((event.phase & kWheelEventPhaseNoEventMask) ||
-        (event.momentum_phase & kWheelEventPhaseNoEventMask))
-      return WebInputEventResult::kNotHandled;
-#endif
-
-    wheel_target_ = FindTargetNode(event, doc, view);
-  }
-
-  LocalFrame* subframe =
-      EventHandlingUtil::SubframeForTargetNode(wheel_target_.Get());
-  if (subframe) {
-    WebInputEventResult result =
-        subframe->GetEventHandler().HandleWheelEvent(event);
-    if (result != WebInputEventResult::kNotHandled)
-      scroll_manager_->SetFrameWasScrolledByUser();
-    return result;
-  }
-
-  if (wheel_target_) {
-    WheelEvent* dom_event =
-        WheelEvent::Create(event, wheel_target_->GetDocument().domWindow());
-    DispatchEventResult dom_event_result =
-        wheel_target_->DispatchEvent(dom_event);
-    if (dom_event_result != DispatchEventResult::kNotCanceled)
-      return EventHandlingUtil::ToWebInputEventResult(dom_event_result);
-  }
-
-  return WebInputEventResult::kNotHandled;
-}
-
-Node* MouseWheelEventManager::FindTargetNode(const WebMouseWheelEvent& event,
-                                             const Document* doc,
-                                             const LocalFrameView* view) {
-  DCHECK(doc && !doc->GetLayoutViewItem().IsNull() && view);
   LayoutPoint v_point =
       view->RootFrameToContents(FlooredIntPoint(event.PositionInRootFrame()));
 
   HitTestRequest request(HitTestRequest::kReadOnly);
   HitTestResult result(request, v_point);
   doc->GetLayoutViewItem().HitTest(result);
 
   Node* node = result.InnerNode();
   // Wheel events should not dispatch to text nodes.
   if (node && node->IsTextNode())
     node = FlatTreeTraversal::Parent(*node);
 
   // If we're over the frame scrollbar, scroll the document.
   if (!node && result.GetScrollbar())
     node = doc->documentElement();
 
-  return node;
+  LocalFrame* subframe = EventHandlingUtil::SubframeForTargetNode(node);
+  if (subframe) {
+    WebInputEventResult result =
+        subframe->GetEventHandler().HandleWheelEvent(event);
+    if (result != WebInputEventResult::kNotHandled)
+      scroll_manager_->SetFrameWasScrolledByUser();
+    return result;
+  }
+
+  if (node) {
+    WheelEvent* dom_event =
+        WheelEvent::Create(event, node->GetDocument().domWindow());
+    DispatchEventResult dom_event_result = node->DispatchEvent(dom_event);
+    if (dom_event_result != DispatchEventResult::kNotCanceled)
+      return EventHandlingUtil::ToWebInputEventResult(dom_event_result);
+  }
+
+  return WebInputEventResult::kNotHandled;
 }
 
 }  // namespace blink