34518947: UIWebView safe area inset constants are not updated on rotation

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Description

Summary:
When rotating the device, it appears that the CSS safe-area-inset constants are not getting updated in UIWebView. They seem to be getting updated after the rotation, but not in time for them to apply to the re-drawn view.

Steps to Reproduce:

1. Load a page with viewport-fit=cover and constant(safe-area-inset-top) into a fullscreen UIWebView on iPhone X in portrait view (example HTML: https://gist.github.com/dpogue/dbfe53aaa2c8ed914c8f2d8fd8beb78a)

2. Rotate the device to landscape view.

3. Rotate the device back to portrait view.

Expected Results:
The safe area constants should be correct for the given view, and update automatically when rotation occurs.

Actual Results:
After rotating to landscape view, the safe-area-inset-top still seems to have a value of 44px.
After rotating back to portrait view, the safe-area-inset-top seems to have a value of 0px.

Version:
iOS 11 GM

Notes:
This is fixed in WKWebView, possibly by this: https://bugs.webkit.org/show_bug.cgi?id=174598 & rdar://problem/33364275

Product Version: iOS 11 GM
Created: 2017-09-19T16:41:16.078000
Originated: 2017-09-19T09:41:00
Open Radar Link: http://www.openradar.me/34518947