Revert "Touchpad scroll latching enabled for Mac behind flag."

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index 452ecc00deba8883d4cbe6b2a78585d36d3ff536..58597f1bdb7cc97a903064a54192aba7e9474ef4 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -133,12 +133,6 @@ cc::ScrollState CreateScrollStateForGesture(const WebGestureEvent& event) {
       scroll_state_data.position_x = event.x;
       scroll_state_data.position_y = event.y;
       scroll_state_data.is_beginning = true;
-      // On Mac, a GestureScrollBegin in the inertial phase indicates a fling
-      // start.
-      if (event.data.scrollBegin.inertialPhase ==
-          WebGestureEvent::MomentumPhase) {
-        scroll_state_data.is_in_inertial_phase = true;
-      }
       break;
     case WebInputEvent::GestureFlingStart:
       scroll_state_data.velocity_x = event.data.flingStart.velocityX;
@@ -497,8 +491,24 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::ScrollByMouseWheel(
         blink::WebGestureDeviceTouchpad,
         cc::MainThreadScrollingReason::kPageBasedScrolling);
     return DID_NOT_HANDLE;
+  } else if (ShouldAnimate(wheel_event.hasPreciseScrollingDeltas)) {
+    cc::InputHandler::ScrollStatus scroll_status =
+        input_handler_->ScrollAnimated(gfx::Point(wheel_event.x, wheel_event.y),
+                                       scroll_delta);
+
+    RecordMainThreadScrollingReasons(
+        blink::WebGestureDeviceTouchpad,
+        scroll_status.main_thread_scrolling_reasons);
+
+    switch (scroll_status.thread) {
+      case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
+        return DID_HANDLE;
+      case cc::InputHandler::SCROLL_IGNORED:
+        return DROP_EVENT;
+      default:
+        return DID_NOT_HANDLE;
+    }
   } else {
-    DCHECK(!ShouldAnimate(wheel_event.hasPreciseScrollingDeltas));
     cc::ScrollStateData scroll_state_begin_data;
     scroll_state_begin_data.position_x = wheel_event.x;
     scroll_state_begin_data.position_y = wheel_event.y;
@@ -632,7 +642,6 @@ InputHandlerProxy::HandleGestureScrollUpdate(
 
   if (ShouldAnimate(gesture_event.data.scrollUpdate.deltaUnits !=
                     blink::WebGestureEvent::ScrollUnits::Pixels)) {
-    DCHECK(!scroll_state.is_in_inertial_phase());
     switch (input_handler_->ScrollAnimated(scroll_point, scroll_delta).thread) {
       case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
         return DID_HANDLE;