MouseWheelEventQueue should respect ScrollBegin/End state from RenderWidgetHost.

content/browser/renderer_host/input/mouse_wheel_event_queue.cc

Index: content/browser/renderer_host/input/mouse_wheel_event_queue.cc
diff --git a/content/browser/renderer_host/input/mouse_wheel_event_queue.cc b/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
index 1728da15397f81f3146534e1220b523969983213..ef0862aa845f6784ef91f40ac4dae0d976dcba3f 100644
--- a/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
+++ b/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
@@ -37,8 +37,6 @@ class QueuedWebMouseWheelEvent : public MouseWheelEventWithLatencyInfo {
 MouseWheelEventQueue::MouseWheelEventQueue(MouseWheelEventQueueClient* client,
                                            bool enable_scroll_latching)
     : client_(client),
-      needs_scroll_begin_(true),
-      needs_scroll_end_(false),
       enable_scroll_latching_(enable_scroll_latching),
       scrolling_device_(blink::kWebGestureDeviceUninitialized) {
   DCHECK(client);
@@ -180,8 +178,9 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
     // because the events generated will be a GSB (non-synthetic) and GSE
     // (non-synthetic). This situation arises when OSX generates double
     // phase end information.
-    bool empty_sequence =
-        !needs_update && needs_scroll_begin_ && current_phase_ended;
+    bool empty_sequence = !needs_update &&
+                          !client_->IsInGestureScrollForTouchpad() &&
+                          current_phase_ended;
 
     if (enable_scroll_latching_) {
       if (event_sent_for_gesture_ack_->event.momentum_phase ==
@@ -192,7 +191,7 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
       }
 
       if (needs_update || !empty_sequence) {
-        if (needs_scroll_begin_) {
+        if (!client_->IsInGestureScrollForTouchpad()) {
           SendScrollBegin(scroll_update, false);
         }
 
@@ -221,7 +220,7 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
 
     } else {  // !enable_scroll_latching_
       if (needs_update || !empty_sequence) {
-        if (needs_scroll_begin_) {
+        if (!client_->IsInGestureScrollForTouchpad()) {
           // If no GSB has been sent, it will be a non-synthetic GSB.
           SendScrollBegin(scroll_update, false);
         } else if (has_phase_info) {
@@ -284,8 +283,6 @@ void MouseWheelEventQueue::OnGestureScrollEvent(
         // Don't send the pending ScrollEnd if a fling is happening.
         // The next wheel event will still need a ScrollBegin.
         scroll_end_timer_.Stop();
-        needs_scroll_begin_ = true;
-        needs_scroll_end_ = false;
       } else {
         scroll_end_timer_.Reset();
       }
@@ -307,7 +304,8 @@ void MouseWheelEventQueue::TryForwardNextEventToRenderer() {
 
 void MouseWheelEventQueue::SendScrollEnd(WebGestureEvent update_event,
                                          bool synthetic) {
-  DCHECK((synthetic && !needs_scroll_end_) || needs_scroll_end_);
+  DCHECK((synthetic && !client_->IsInGestureScrollForTouchpad()) ||
+         client_->IsInGestureScrollForTouchpad());
 
   WebGestureEvent scroll_end(update_event);
   scroll_end.SetTimeStampSeconds(
@@ -320,13 +318,9 @@ void MouseWheelEventQueue::SendScrollEnd(WebGestureEvent update_event,
   scroll_end.data.scroll_end.delta_units =
       update_event.data.scroll_update.delta_units;
 
-  if (!synthetic) {
-    needs_scroll_begin_ = true;
-    needs_scroll_end_ = false;
+  if (!synthetic && scroll_end_timer_.IsRunning())
+    scroll_end_timer_.Reset();
 
-    if (scroll_end_timer_.IsRunning())
-      scroll_end_timer_.Reset();
-  }
   client_->ForwardGestureEventWithLatencyInfo(
       scroll_end, ui::LatencyInfo(ui::SourceEventType::WHEEL));
 }
@@ -334,7 +328,8 @@ void MouseWheelEventQueue::SendScrollEnd(WebGestureEvent update_event,
 void MouseWheelEventQueue::SendScrollBegin(
     const WebGestureEvent& gesture_update,
     bool synthetic) {
-  DCHECK((synthetic && !needs_scroll_begin_) || needs_scroll_begin_);
+  DCHECK((synthetic && client_->IsInGestureScrollForTouchpad()) ||
+         !client_->IsInGestureScrollForTouchpad());
 
   WebGestureEvent scroll_begin(gesture_update);
   scroll_begin.SetType(WebInputEvent::kGestureScrollBegin);
@@ -349,8 +344,6 @@ void MouseWheelEventQueue::SendScrollBegin(
   scroll_begin.data.scroll_begin.delta_hint_units =
       gesture_update.data.scroll_update.delta_units;
 
-  needs_scroll_begin_ = false;
-  needs_scroll_end_ = true;
   client_->ForwardGestureEventWithLatencyInfo(
       scroll_begin, ui::LatencyInfo(ui::SourceEventType::WHEEL));
 }