Open Radar

 
# Title

Auto Layout fails when UINavigationController is added as a child ViewController if `scrollViewDidScroll:` calls `topLayoutGuide`

# Description

When a UINavigationController is added as a child ViewController, the view controller in the navigation controller will experience issues with Auto Layout if it has a scroll view whose delegat's `scrollViewDidScroll:` method calls into the UIViewController's `topLayoutGuide` property.

In that situation, views with auto layout constraints set up will all have a frame with size (0,0):

```
(lldb) po [0x7fb8e99b3700 subviews]
<__NSArrayM 0x7fb8e99c1650>(
<UIScrollView: 0x7fb8ea865200; frame = (364 492; 0 0); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x7fb8e99bcae0>; layer = <CALayer: 0x7fb8e999fb90>; contentOffset: {0, 0}; contentSize: {0, 0}>,
<UIView: 0x7fb8e9a01fc0; frame = (0 0; 0 0); layer = <CALayer: 0x7fb8e9a01f30>>
)
```

# Steps to Reproduce

1. Create a UIViewController containing a scrollView, with its delegate's scrollViewDidScroll method calling `topLayoutGuide` on the UIViewController
2. Create a UINavigationController with the controller created in (1) as its root
3. Add the UINavigationController from (2) as a child view controller to an existing view controller

# Expected Results

The subviews within the view of the UIViewController created in (1) should be laid out as expected, according to the Auto Layout constraints they were created with.

# Actual Results

All the subviews have size (0, 0).

# Configuration

iPad Air, iPad Mini, iPhone 6

# Version & Build

iOS 9 and above

# Sample Project

https://www.dropbox.com/s/npjq21zk7nd284h/ViewController.m?dl=0
https://www.dropbox.com/s/mhnjj3zfqird1vj/NavControllerTester.zip?dl=0