[ASTableView] Add retainedLayer a la collection view (#1896)

AsyncDisplayKit/ASTableView.mm

@@ -11,6 +11,7 @@
 #import "ASTableViewInternal.h"
 
 #import "ASAssert.h"
+#import "ASAvailability.h"
 #import "ASBatchFetching.h"
 #import "ASCellNode+Internal.h"
 #import "ASChangeSetDataController.h"
@@ -111,6 +112,15 @@ @interface ASTableView () <ASRangeControllerDataSource, ASRangeControllerDelegat
   CGFloat _contentOffsetAdjustment;
 
   CGPoint _deceleratingVelocity;
+
+  /**
+   * Our layer, retained. Under iOS < 9, when table views are removed from the hierarchy,
+   * their layers may be deallocated and become dangling pointers. This puts the table view
+   * into a very dangerous state where pretty much any call will crash it. So we manually retain our layer.
+   *
+   * You should never access this, and it will be nil under iOS >= 9.
+   */
+  CALayer *_retainedLayer;
 
   CGFloat _nodesConstrainedWidth;
   BOOL _ignoreNodesConstrainedWidthChange;
@@ -235,6 +245,10 @@ - (instancetype)_initWithFrame:(CGRect)frame style:(UITableViewStyle)style dataC
     self.strongTableNode = tableNode;
   }
 
+  if (!AS_AT_LEAST_IOS9) {
+    _retainedLayer = self.layer;
+  }
+
   return self;
 }