Cherry-pick 273989@main (439730f). https://bugs.webkit.org/show_bug.c…

…gi?id=268603

    Document::isFullyActive should return true for root frames in addition to main frames
    https://bugs.webkit.org/show_bug.cgi?id=268603
    rdar://122164616

    Reviewed by Charlie Wolfe.

    Before this change XMLHttpRequest::open would always throw an exception if called from a
    cross-site iframe with site isolation enabled.  This will probably fix a lot of behavior.

    * LayoutTests/platform/mac-site-isolation/TestExpectations:
    * Source/WebCore/dom/Document.cpp:
    (WebCore::Document::isFullyActive const):

    Canonical link: https://commits.webkit.org/273989@main

Canonical link: https://commits.webkit.org/266719.362@webkitglib/2.42

Source/WebCore/dom/Document.cpp

@@ -3136,11 +3136,11 @@ bool Document::isFullyActive() const
     if (!frame || frame->document() != this)
         return false;
 
-    if (frame->isMainFrame())
+    auto* parentFrame = dynamicDowncast<LocalFrame>(frame->tree().parent());
+    if (!parentFrame)
         return true;
 
-    auto* parentFrame = dynamicDowncast<LocalFrame>(frame->tree().parent());
-    return parentFrame && parentFrame->document() && parentFrame->document()->isFullyActive();
+    return parentFrame->document() && parentFrame->document()->isFullyActive();
 }
 
 void Document::detachParser()