iOS 17: History back sometimes scrolls to top of the page (with app banner)

[smfr]

2bafc1b

iOS 17: History back sometimes scrolls to top of the page (with app banner)
https://bugs.webkit.org/show_bug.cgi?id=231563
rdar://117107620

Reviewed by Tim Horton.

Sometimes, navigating back to a page on iOS would fail to restore the scroll position to the correct
location. This happened when `WebPage::restorePageState()` hit the second mismatched
`minimumLayoutSizeInScrollViewCoordinates` clause, which made use of
`historyItem.unobscuredContentRect()`. This could happen when MobileSafari app banners were hidden
or shown. `historyItem.unobscuredContentRect()` had the wrong value in this case, containing a rect
that had a 0,0 location which triggered a scroll back to the top.

`historyItem.unobscuredContentRect()` was wrong because it was set in
`HistoryController::saveScrollPositionAndViewStateToItem()` which runs after we've reset the content
size in preparation for the navigation; note that this function uses
`frameView->cachedScrollPosition()`. So the fix is to cache `unobscuredContentRect()` and
`exposedContentRect()` in the same way.

This is messy; ScrollView shouldn't be in the business of storing caches related to page navigation,
but fixing that is out of scope for this change.

The API test navigates and goes back with a view size change, which triggers the bug.

Also add some release logging to help diagnose scroll restoration bugs.

* Source/WebCore/dom/Document.cpp:
(WebCore::Document::setBackForwardCacheState):
* Source/WebCore/loader/HistoryController.cpp:
(WebCore::FrameLoader::HistoryController::saveScrollPositionAndViewStateToItem):
* Source/WebCore/platform/ScrollView.cpp:
(WebCore::ScrollView::cacheCurrentScrollState):
* Source/WebCore/platform/ScrollView.h:
(WebCore::ScrollView::cachedUnobscuredContentRect const):
(WebCore::ScrollView::cachedExposedContentRect const):
(WebCore::ScrollView::cacheCurrentScrollPosition): Deleted.
* Tools/TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj:
* Tools/TestWebKitAPI/Tests/ios/ScrollViewInsetTests.mm:
(TestWebKitAPI::TEST):
* Tools/TestWebKitAPI/ios/scrollable-page.html: Added.

Canonical link: https://commits.webkit.org/269611@main

b6b3e75

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	🧪 api-gtk
	🛠 tv	🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
✅ 🛠 🧪 merge	🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 451a25d)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	⏳ 🧪 wpe-wk2
✅ 🧪 webkitperl	⏳ 🧪 ios-wk2	🧪 api-mac	✅ 🛠 gtk
	⏳ 🧪 ios-wk2-wpt	🧪 mac-wk1	⏳ 🧪 gtk-wk2
⏳ 🛠 🧪 jsc	🧪 api-ios	🧪 mac-wk2	🧪 api-gtk
	🛠 tv	🧪 mac-AS-debug-wk2	⏳ 🛠 jsc-armv7
	⏳ 🛠 tv-sim		⏳ 🧪 jsc-armv7-tests
	⏳ 🛠 watch
	⏳ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 66d8e6c)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	🧪 api-ios	✅ 🧪 mac-wk2	🧪 api-gtk
	✅ 🛠 tv	⏳ 🧪 mac-AS-debug-wk2
	❌ 🛠 tv-sim
	❌ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash b6b3e75)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	🧪 api-gtk
	🛠 tv	🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
✅ 🛠 🧪 merge	🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 269611@main (2bafc1b): https://commits.webkit.org/269611@main

Reviewed commits have been landed. Closing PR #19324 and removing active labels.