RELEASE_ASSERT(isUIThread()) in WebKit::allDataStores

[Daniel]

We are getting a significant amount of crashes with this stack trace:

Crashed: WebThread
0  WebKit                         0x17c90 WTFCrashWithInfo(int, char const*, char const*, int) + 20
1  WebKit                         0x6af064 WebKit::allDataStores() + 76
2  WebKit                         0x6aef78 WebKit::WebsiteDataStore::forEachWebsiteDataStore(WTF::Function<void (WebKit::WebsiteDataStore&)>&&) + 28
3  WebKit                         0x3f3a88 WebKit::WebProcessPool::updateProcessSuppressionState() + 112
4  WebKit                         0x59f168 WebKit::WebPageProxy::updateThrottleState() + 192
5  WebKit                         0x5ae300 WebKit::WebPageProxy::dispatchActivityStateChange() + 1008
6  CoreFoundation                 0x410c4 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 36
7  CoreFoundation                 0x10080 __CFRunLoopDoObservers + 592
8  CoreFoundation                 0x1ec1c CFRunLoopRunSpecific + 684
9  WebCore                        0xbe9d3c <redacted> + 760
10 libsystem_pthread.dylib        0x19ac _pthread_start + 148
11 libsystem_pthread.dylib        0xe68 thread_start + 8

All the other threads are idle at the time of the crash.

The crash seems to affect iOS 15.2.0+ and 16.0.0.
It started appearing in late July 2022 for us.

[Alexey Proskuryakov]

The only RELEASE_ASSERT in this function is:

    RELEASE_ASSERT(isUIThread());

[Radar WebKit Bug Importer]

<rdar://problem/98596494>