Disable UICollectionView prefetching to improve scroll performance (#2861)

Author: Adlai Holler

AsyncDisplayKit/ASCollectionView.mm

@@ -280,7 +280,15 @@ - (instancetype)_initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionV
 {
   if (!(self = [super initWithFrame:frame collectionViewLayout:layout]))
     return nil;
-  
+
+  // Disable UICollectionView prefetching.
+  // Experiments done by Instagram show that this option being YES (default)
+  // when unused causes a significant hit to scroll performance.
+  // https://github.com/Instagram/IGListKit/issues/318
+  if (AS_AT_LEAST_IOS10) {
+    self.prefetchingEnabled = NO;
+  }
+
   _layoutController = [[ASCollectionViewLayoutController alloc] initWithCollectionView:self];
 
   _rangeController = [[ASRangeController alloc] init];