Boundary test of removing all IGListAdapter animation

Summary:
# Context

We've seen several experiments in which disabling standard-update animation yielded significant app-value wins. Overall there is a trend of moving towards snappier

- Reels grid disabled animation, led to vpvd wins
- Home feed disabled update animations -- led to Session and revenue wins

# This diff

From IGListAdapter+Common, create a kill switch to disable all animation. Potentially use this flag to dogfood and see where we have unnecessary animation.

Differential Revision: D54388375

fbshipit-source-id: a46c60944317db5deeceaac6d0baed71104d0c34

Source/IGListDiffKit/IGListExperiments.h

@@ -21,7 +21,9 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
     /// Throw NSInternalInconsistencyException during an update
     IGListExperimentThrowOnInconsistencyException = 1 << 3,
     /// Test keeping a strong pointer to the collectionView.dataSource during a batch update to avoid a crash
-    IGListExperimentKeepPointerToCollectionViewDataSource = 1 << 4
+    IGListExperimentKeepPointerToCollectionViewDataSource = 1 << 4,
+    /// Test keeping disable all animation on updates
+    IGListExperimentDisableAnimationOnUpdates= 1 << 5
 };
 
 /**

Source/IGListKit/IGListAdapter.h

@@ -103,6 +103,7 @@ NS_SWIFT_NAME(ListAdapter)
  */
 @property (nonatomic, assign) IGListExperiment experiments;
 
+
 /**
  Initializes a new `IGListAdapter` object.
 

Source/IGListKit/IGListAdapter.m

@@ -414,7 +414,7 @@ - (void)performUpdatesAnimated:(BOOL)animated completion:(IGListUpdaterCompletio
             [strongSelf _updateWithData:data];
         }
     };
-
+    const BOOL shouldAnimateUpdates =  animated && !IGListExperimentEnabled(self.experiments, IGListExperimentDisableAnimationOnUpdates);
     IGListUpdaterCompletion outerCompletionBlock = ^(BOOL finished){
         __typeof__(self) strongSelf = weakSelf;
         if (strongSelf == nil) {
@@ -424,7 +424,7 @@ - (void)performUpdatesAnimated:(BOOL)animated completion:(IGListUpdaterCompletio
 
         // release the previous items
         strongSelf.previousSectionMap = nil;
-        [strongSelf _notifyDidUpdate:IGListAdapterUpdateTypePerformUpdates animated:animated];
+        [strongSelf _notifyDidUpdate:IGListAdapterUpdateTypePerformUpdates animated:shouldAnimateUpdates];
         IGLK_BLOCK_CALL_SAFE(completion,finished);
         [strongSelf _exitBatchUpdates];
     };
@@ -686,7 +686,7 @@ - (IGListTransitionData *)_generateTransitionDataWithObjects:(NSArray *)objects
                     dataSource, object);
             return;
         }
-        
+
         if ([sectionController isMemberOfClass:[IGListSectionController class]]) {
             // If IGListSectionController is not subclassed, it could be a side effect of a problem. For example, nothing stops
             // dataSource from returning a plain IGListSectionController if it doesn't recognize the object type, instead of throwing.
@@ -1367,7 +1367,7 @@ - (void)insertInSectionController:(IGListSectionController *)sectionController a
 
     NSArray *indexPaths = [self indexPathsFromSectionController:sectionController indexes:indexes usePreviousIfInUpdateBlock:NO];
     [self.updater insertItemsIntoCollectionView:collectionView indexPaths:indexPaths];
-    
+
     if (![self isInDataUpdateBlock]) {
         [self _updateBackgroundView];
     }
@@ -1386,7 +1386,7 @@ - (void)deleteInSectionController:(IGListSectionController *)sectionController a
 
     NSArray *indexPaths = [self indexPathsFromSectionController:sectionController indexes:indexes usePreviousIfInUpdateBlock:YES];
     [self.updater deleteItemsFromCollectionView:collectionView indexPaths:indexPaths];
-    
+
     if (![self isInDataUpdateBlock]) {
         [self _updateBackgroundView];
     }