Bug 1689052 - Only get a docshell when the document is visible. r=rickiedennehy

Differential Revision: https://phabricator.services.mozilla.com/D103149

dom/base/Document.cpp

@@ -15228,7 +15228,9 @@ void Document::SetContentTypeInternal(const nsACString& aType) {
 
 nsILoadContext* Document::GetLoadContext() const { return mDocumentContainer; }
 
-nsIDocShell* Document::GetDocShell() const { return mDocumentContainer; }
+nsIDocShell* Document::GetDocShell() const {
+  return mVisible ? mDocumentContainer : nullptr;
+}
 
 void Document::SetStateObject(nsIStructuredCloneContainer* scContainer) {
   mStateObjectContainer = scContainer;