Bug 1867152 - Fix the assertion in nsPresContext::UserInputEventsAllowed r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D196106

dom/base/Document.cpp

@@ -1309,6 +1309,7 @@ Document::Document(const char* aContentType)
       mMayNeedFontPrefsUpdate(true),
       mMathMLEnabled(false),
       mIsInitialDocumentInWindow(false),
+      mIsEverInitialDocumentInWindow(false),
       mIgnoreDocGroupMismatches(false),
       mLoadedAsData(false),
       mAddedToMemoryReportingAsDataDocument(false),
@@ -18689,6 +18690,10 @@ nsIPrincipal* Document::GetPrincipalForPrefBasedHacks() const {
 void Document::SetIsInitialDocument(bool aIsInitialDocument) {
   mIsInitialDocumentInWindow = aIsInitialDocument;
 
+  if (aIsInitialDocument && !mIsEverInitialDocumentInWindow) {
+    mIsEverInitialDocumentInWindow = aIsInitialDocument;
+  }
+
   // Asynchronously tell the parent process that we are, or are no longer, the
   // initial document. This happens async.
   if (auto* wgc = GetWindowGlobalChild()) {

dom/base/Document.h

@@ -994,6 +994,12 @@ class Document : public nsINode,
    */
   bool IsInitialDocument() const { return mIsInitialDocumentInWindow; }
 
+  /**
+   * Ask this document whether it has ever been a initial document in its
+   * window.
+   */
+  bool IsEverInitialDocument() const { return mIsEverInitialDocumentInWindow; }
+
   /**
    * Tell this document that it's the initial document in its window.  See
    * comments on mIsInitialDocumentInWindow for when this should be called.
@@ -4555,6 +4561,11 @@ class Document : public nsINode,
   // document in it.
   bool mIsInitialDocumentInWindow : 1;
 
+  // True if this document has ever been the initial document for a window. This
+  // is useful to determine if a document that was the initial document at one
+  // point, and became non-initial later.
+  bool mIsEverInitialDocumentInWindow : 1;
+
   bool mIgnoreDocGroupMismatches : 1;
 
   // True if we're loaded as data and therefor has any dangerous stuff, such

layout/base/nsPresContext.cpp

@@ -1237,7 +1237,7 @@ bool nsPresContext::UserInputEventsAllowed() {
   }
 
   // Special document
-  if (Document()->IsInitialDocument()) {
+  if (Document()->IsEverInitialDocument()) {
     return true;
   }