Add option to disable sending scroll events to Paper

Summary:
Changelog: [internal]

Originally added in D17814260 (https://github.com/facebook/react-native/commit/ffc7ec992c66417039b0fa14f1afd54a9cd2f882) to make parallax effect work in Dating.

This diff hides it behind a flag so we can properly evaluate what's the cost of sending scroll events to Paper.

Reviewed By: JoshuaGross

Differential Revision: D28608283

fbshipit-source-id: fa4d8944ad6b5e767363e231942f13fec9d18cb5

React/Base/RCTConstants.h

@@ -17,6 +17,12 @@ RCT_EXTERN NSString *const RCTUserInterfaceStyleDidChangeNotificationTraitCollec
 RCT_EXTERN BOOL RCTExperimentGetOnDemandViewMounting(void);
 RCT_EXTERN void RCTExperimentSetOnDemandViewMounting(BOOL value);
 
+/*
+ * Allows sending scroll events to Paper.
+ */
+RCT_EXTERN BOOL RCTExperimentGetSendScrollEventToPaper(void);
+RCT_EXTERN void RCTExperimentSetSendScrollEventToPaper(BOOL value);
+
 /*
  * Preemptive View Allocation
  */

React/Base/RCTConstants.m

@@ -25,6 +25,21 @@ void RCTExperimentSetOnDemandViewMounting(BOOL value)
   RCTExperimentOnDemandViewMounting = value;
 }
 
+/*
+ * Send scroll events to Paper.
+ */
+static BOOL RCTExperimentSendScrollEventToPaper = YES;
+
+BOOL RCTExperimentGetSendScrollEventToPaper()
+{
+  return RCTExperimentSendScrollEventToPaper;
+}
+
+void RCTExperimentSetSendScrollEventToPaper(BOOL value)
+{
+  RCTExperimentSendScrollEventToPaper = value;
+}
+
 /*
  * Preemptive View Allocation
  */

React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm

@@ -87,6 +87,7 @@ static void RCTSendPaperScrollEvent_DEPRECATED(UIScrollView *scrollView, NSInteg
   BOOL _isUserTriggeredScrolling;
 
   BOOL _isOnDemandViewMountingEnabled;
+  BOOL _sendScrollEventToPaper;
   CGPoint _contentOffsetWhenClipped;
   NSMutableArray<UIView<RCTComponentViewProtocol> *> *_childComponentViews;
 }
@@ -106,6 +107,7 @@ static void RCTSendPaperScrollEvent_DEPRECATED(UIScrollView *scrollView, NSInteg
     _props = defaultProps;
 
     _isOnDemandViewMountingEnabled = RCTExperimentGetOnDemandViewMounting();
+    _sendScrollEventToPaper = RCTExperimentGetSendScrollEventToPaper();
     _childComponentViews = [[NSMutableArray alloc] init];
 
     _scrollView = [[RCTEnhancedScrollView alloc] initWithFrame:self.bounds];
@@ -419,7 +421,9 @@ static void RCTSendPaperScrollEvent_DEPRECATED(UIScrollView *scrollView, NSInteg
     }
     // Once Fabric implements proper NativeAnimationDriver, this should be removed.
     // This is just a workaround to allow animations based on onScroll event.
-    RCTSendPaperScrollEvent_DEPRECATED(scrollView, self.tag);
+    if (_sendScrollEventToPaper) {
+      RCTSendPaperScrollEvent_DEPRECATED(scrollView, self.tag);
+    }
   }
 
   [self _remountChildrenIfNeeded];

React/Fabric/RCTSurfacePresenter.mm

@@ -257,6 +257,10 @@ static BackgroundExecutor RCTGetBackgroundExecutor()
     RCTExperimentSetOnDemandViewMounting(YES);
   }
 
+  if (reactNativeConfig && reactNativeConfig->getBool("react_fabric:disable_sending_scroll_events_to_paper")) {
+    RCTExperimentSetSendScrollEventToPaper(NO);
+  }
+
   if (reactNativeConfig && reactNativeConfig->getBool("react_fabric:preemptive_view_allocation_disabled_ios")) {
     RCTExperimentSetPreemptiveViewAllocationDisabled(YES);
   }