Crash in ViewTransition::create

https://bugs.webkit.org/show_bug.cgi?id=265806
rdar://119142736

Reviewed by Tim Nguyen.

If there is no global object, return null.  This matches the behavior of Chromium.

* LayoutTests/fast/dom/view-transition-without-global-object-expected.txt: Added.
* LayoutTests/fast/dom/view-transition-without-global-object.html: Added.
* Source/WebCore/dom/Document.cpp:
(WebCore::Document::startViewTransition):
* Source/WebCore/dom/Document.h:

Canonical link: https://commits.webkit.org/272959@main

LayoutTests/fast/dom/view-transition-without-global-object-expected.txt

@@ -0,0 +1,2 @@
+ALERT: result should be null:null
+This test passes if it does not crash.

LayoutTests/fast/dom/view-transition-without-global-object.html

@@ -0,0 +1,6 @@
+<script>
+if (window.testRunner) { testRunner.dumpAsText() }
+let d = document.implementation.createDocument("", null);
+alert("result should be null:" + d.startViewTransition(()=>{alert('callback should not be called')}))
+</script>
+This test passes if it does not crash.

Source/WebCore/dom/Document.cpp

@@ -9862,16 +9862,19 @@ void Document::setHasViewTransitionPseudoElementTree(bool value)
     m_hasViewTransitionPseudoElementTree = value;
 }
 
-Ref<ViewTransition> Document::startViewTransition(RefPtr<ViewTransitionUpdateCallback>&& updateCallback)
+RefPtr<ViewTransition> Document::startViewTransition(RefPtr<ViewTransitionUpdateCallback>&& updateCallback)
 {
+    if (!globalObject())
+        return nullptr;
+
     Ref viewTransition = ViewTransition::create(*this, WTFMove(updateCallback));
 
     if (RefPtr activeViewTransition = m_activeViewTransition)
         activeViewTransition->skipViewTransition(Exception { ExceptionCode::AbortError, "Old view transition aborted by new view transition."_s });
 
     setActiveViewTransition(WTFMove(viewTransition));
     scheduleRenderingUpdate(RenderingUpdateStep::PerformPendingViewTransitions);
-    return *m_activeViewTransition;
+    return m_activeViewTransition;
 }
 
 void Document::performPendingViewTransitions()

Source/WebCore/dom/Document.h

@@ -1625,7 +1625,7 @@ class Document
     void unobserveForContainIntrinsicSize(Element&);
     void resetObservationSizeForContainIntrinsicSize(Element&);
 
-    Ref<ViewTransition> startViewTransition(RefPtr<ViewTransitionUpdateCallback>&& = nullptr);
+    RefPtr<ViewTransition> startViewTransition(RefPtr<ViewTransitionUpdateCallback>&& = nullptr);
     ViewTransition* activeViewTransition() const;
     void setActiveViewTransition(RefPtr<ViewTransition>&&);