Description:
imported/w3c/web-platform-tests/workers/modules/dedicated-worker-import-referrer.html

After consistently passing the test begins to flaky crash starting at 253762@main.

REPRODUCTION STEPS
I can reproduce this on 253762@main but cannot reproduce it on 253761@main or earlier.

Command: 
run-webkit-tests --debug -1 --exit-after-n-failures 1 --exit-after-n-crashes-or-timeouts 1 --iterations 50 -f --no-retry  --child-processes 1 --test-list <test list attached>

Result: 
Regressions: Unexpected crashes (1)
  imported/w3c/web-platform-tests/workers/modules/dedicated-worker-import-referrer.html [ Crash ]

History:
https://results.webkit.org/?suite=layout-tests&test=imported%2Fw3c%2Fweb-platform-tests%2Fworkers%2Fmodules%2Fdedicated-worker-import-referrer.html&platform=mac&style=debug&flavor=wk1

Crash Log:
Thread 0 Crashed::   Dispatch queue: com.apple.main-thread
0   com.apple.WebKitLegacy        	       0x10fb3e260        WTF::HashTable<WebCore::SecurityOriginData, WTF::KeyValuePair<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > >, WTF::KeyValuePairKeyExtractor<WTF::KeyValuePair<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > > >, WTF::DefaultHash<WebCore::SecurityOriginData>, WTF::HashMap<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> >, WTF::DefaultHash<WebCore::SecurityOriginData>, WTF::HashTraits<WebCore::SecurityOriginData>, WTF::HashTraits<WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > >, WTF::HashTableTraits>::KeyValuePairTraits, WTF::HashTraits<WebCore::SecurityOriginData> >::keyCount() const
1   com.apple.WebKitLegacy        	       0x10fb3e514        WTF::HashTable<WebCore::SecurityOriginData, WTF::KeyValuePair<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > >, WTF::KeyValuePairKeyExtractor<WTF::KeyValuePair<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > > >, WTF::DefaultHash<WebCore::SecurityOriginData>, WTF::HashMap<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> >, WTF::DefaultHash<WebCore::SecurityOriginData>, WTF::HashTraits<WebCore::SecurityOriginData>, WTF::HashTraits<WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > >, WTF::HashTableTraits>::KeyValuePairTraits, WTF::HashTraits<WebCore::SecurityOriginData> >::isEmpty() const
2   com.apple.WebKitLegacy        	       0x10fb408c8        WTF::HashTable<WebCore::SecurityOriginData, WTF::KeyValuePair<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > >, WTF::KeyValuePairKeyExtractor<WTF::KeyValuePair<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > > >, WTF::DefaultHash<WebCore::SecurityOriginData>, WTF::HashMap<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> >, WTF::DefaultHash<WebCore::SecurityOriginData>, WTF::HashTraits<WebCore::SecurityOriginData>, WTF::HashTraits<WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > >, WTF::HashTableTraits>::KeyValuePairTraits, WTF::HashTraits<WebCore::SecurityOriginData> >::begin()
3   com.apple.WebKitLegacy        	       0x10fb36848        WTF::HashMap<WebCore::SecurityOriginData, WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> >, WTF::DefaultHash<WebCore::SecurityOriginData>, WTF::HashTraits<WebCore::SecurityOriginData>, WTF::HashTraits<WTF::RefPtr<WebCore::StorageNamespace, WTF::RawPtrTraits<WebCore::StorageNamespace>, WTF::DefaultRefDerefTraits<WebCore::StorageNamespace> > >, WTF::HashTableTraits>::begin()
4   com.apple.WebKitLegacy        	       0x10fb365c0        WebKit::WebStorageNamespaceProvider::copySessionStorageNamespace(WebCore::Page&, WebCore::Page&)
5   com.apple.WebCore             	       0x1348ce850        WebCore::Chrome::createWindow(WebCore::Frame&, WebCore::WindowFeatures const&, WebCore::NavigationAction const&) const
6   com.apple.WebCore             	       0x1347222f6        WebCore::createWindow(WebCore::Frame&, WebCore::Frame&, WebCore::FrameLoadRequest&&, WebCore::WindowFeatures&, bool&)
7   com.apple.WebCore             	       0x1348f5d36        WebCore::DOMWindow::createWindow(WTF::String const&, WTF::AtomString const&, WebCore::WindowFeatures const&, WebCore::DOMWindow&, WebCore::Frame&, WebCore::Frame&, WTF::Function<void (WebCore::DOMWindow&)> const&)
8   com.apple.WebCore             	       0x1348f709c        WebCore::DOMWindow::open(WebCore::DOMWindow&, WebCore::DOMWindow&, WTF::String const&, WTF::AtomString const&, WTF::String const&)
9   com.apple.WebCore             	       0x130c52bd0        WebCore::jsDOMWindowInstanceFunction_openBody(JSC::JSGlobalObject*, JSC::CallFrame*, WebCore::JSDOMWindow*)
10  com.apple.WebCore             	       0x130c5242e        long long WebCore::IDLOperation<WebCore::JSDOMWindow>::call<&(WebCore::jsDOMWindowInstanceFunction_openBody(JSC::JSGlobalObject*, JSC::CallFrame*, WebCore::JSDOMWindow*)), (WebCore::CastedThisErrorBehavior)0>(JSC::JSGlobalObject&, JSC::CallFrame&, char const*)