Fix retain cycle between shimmering layer and the shimmer animation.

CAAnimation retains its delegate, so only set the delegate on the one
animation it's needed on. Avoiding setting it on the indefinite slide
animation avoids the retain cycle. Since the fade animations are not
infinitely repeated, they will be cleaned up after completion.

FBShimmering/FBShimmeringLayer.m

@@ -47,10 +47,9 @@ static void FBShimmeringLayerAnimationApplyDragCoefficient(CAAnimation *animatio
 static NSString *const kFBFadeAnimationKey = @"fade";
 static NSString *const kFBEndFadeAnimationKey = @"fade-end";
 
-static CABasicAnimation *fade_animation(id delegate, CALayer *layer, CGFloat opacity, CFTimeInterval duration)
+static CABasicAnimation *fade_animation(CALayer *layer, CGFloat opacity, CFTimeInterval duration)
 {
   CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
-  animation.delegate = delegate;
   animation.fromValue = @([(layer.presentationLayer ?: layer) opacity]);
   animation.toValue = @(opacity);
   animation.fillMode = kCAFillModeBoth;
@@ -60,22 +59,9 @@ static void FBShimmeringLayerAnimationApplyDragCoefficient(CAAnimation *animatio
   return animation;
 }
 
-static CABasicAnimation *shimmer_begin_fade_animation(id delegate, CALayer *layer, CGFloat opacity, CGFloat duration)
-{
-  return fade_animation(delegate, layer, opacity, duration);
-}
-
-static CABasicAnimation *shimmer_end_fade_animation(id delegate, CALayer *layer, CGFloat opacity, CGFloat duration)
-{
-  CABasicAnimation *animation = fade_animation(delegate, layer, opacity, duration);
-  [animation setValue:@YES forKey:kFBEndFadeAnimationKey];
-  return animation;
-}
-
-static CABasicAnimation *shimmer_slide_animation(id delegate, CFTimeInterval duration, FBShimmerDirection direction)
+static CABasicAnimation *shimmer_slide_animation(CFTimeInterval duration, FBShimmerDirection direction)
 {
   CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"position"];
-  animation.delegate = delegate;
   animation.toValue = [NSValue valueWithCGPoint:CGPointZero];
   animation.duration = duration;
   animation.repeatCount = HUGE_VALF;
@@ -410,7 +396,9 @@ - (void)_updateShimmering
       }
 
       // fade in text at slideEndTime
-      CABasicAnimation *fadeInAnimation = shimmer_end_fade_animation(self, _maskLayer.fadeLayer, 1.0, _shimmeringEndFadeDuration);
+      CABasicAnimation *fadeInAnimation = fade_animation(_maskLayer.fadeLayer, 1.0, _shimmeringEndFadeDuration);
+      fadeInAnimation.delegate = self;
+      [fadeInAnimation setValue:@YES forKey:kFBEndFadeAnimationKey];
       fadeInAnimation.beginTime = slideEndTime;
       [_maskLayer.fadeLayer addAnimation:fadeInAnimation forKey:kFBFadeAnimationKey];
 
@@ -421,7 +409,7 @@ - (void)_updateShimmering
     // fade out text, optionally animated
     CABasicAnimation *fadeOutAnimation = nil;
     if (_shimmeringBeginFadeDuration > 0.0 && !disableActions) {
-      fadeOutAnimation = shimmer_begin_fade_animation(self, _maskLayer.fadeLayer, 0.0, _shimmeringBeginFadeDuration);
+      fadeOutAnimation = fade_animation(_maskLayer.fadeLayer, 0.0, _shimmeringBeginFadeDuration);
       [_maskLayer.fadeLayer addAnimation:fadeOutAnimation forKey:kFBFadeAnimationKey];
     } else {
       BOOL innerDisableActions = [CATransaction disableActions];
@@ -451,7 +439,7 @@ - (void)_updateShimmering
       [_maskLayer addAnimation:shimmer_slide_repeat(slideAnimation, animationDuration, _shimmeringDirection) forKey:kFBShimmerSlideAnimationKey];
     } else {
       // add slide animation
-      slideAnimation = shimmer_slide_animation(self, animationDuration, _shimmeringDirection);
+      slideAnimation = shimmer_slide_animation(animationDuration, _shimmeringDirection);
       slideAnimation.fillMode = kCAFillModeForwards;
       slideAnimation.removedOnCompletion = NO;
       if (_shimmeringBeginTime == FBShimmerDefaultBeginTime) {