Bug 1736570 - Avoid DocumentChannel for nsParser-created initial about:blank replacement. r=nika,smaug

Differential Revision: https://phabricator.services.mozilla.com/D135106

docshell/base/nsDocShell.h

@@ -501,7 +501,8 @@ class nsDocShell final : public nsDocLoader,
       mozilla::dom::BrowsingContext* aBrowsingContext, uint32_t aLoadType);
 
   void SetLoadingSessionHistoryInfo(
-      const mozilla::dom::LoadingSessionHistoryInfo& aLoadingInfo);
+      const mozilla::dom::LoadingSessionHistoryInfo& aLoadingInfo,
+      bool aNeedToReportActiveAfterLoadingBecomesActive = false);
   const mozilla::dom::LoadingSessionHistoryInfo*
   GetLoadingSessionHistoryInfo() {
     return mLoadingEntry.get();
@@ -675,6 +676,12 @@ class nsDocShell final : public nsDocLoader,
       nsIURI* aCurrentURI, nsIReferrerInfo* aReferrerInfo,
       bool aNotifiedBeforeUnloadListeners = false);
 
+ public:
+  bool IsAboutBlankLoadOntoInitialAboutBlank(nsIURI* aURI,
+                                             bool aInheritPrincipal,
+                                             nsIPrincipal* aPrincipalToInherit);
+
+ private:
   //
   // URI Load
   //
@@ -1213,7 +1220,9 @@ class nsDocShell final : public nsDocLoader,
   // These are only set when fission.sessionHistoryInParent is set.
   mozilla::UniquePtr<mozilla::dom::SessionHistoryInfo> mActiveEntry;
   bool mActiveEntryIsLoadingFromSessionHistory = false;
-  // mLoadingEntry is set when we're about to start loading.
+  // mLoadingEntry is set when we're about to start loading. Whenever
+  // setting mLoadingEntry, be sure to also set
+  // mNeedToReportActiveAfterLoadingBecomesActive.
   mozilla::UniquePtr<mozilla::dom::LoadingSessionHistoryInfo> mLoadingEntry;
 
   // Holds a weak pointer to a RestorePresentationEvent object if any that
@@ -1362,6 +1371,12 @@ class nsDocShell final : public nsDocLoader,
    * a possible history load. Used only with iframes.
    */
   bool mCheckingSessionHistory : 1;
+
+  // Whether mBrowsingContext->SetActiveSessionHistoryEntry() needs to be called
+  // when the loading entry becomes the active entry. This is used for the
+  // initial about:blank-replacing about:blank in order to make the history
+  // length WPTs pass.
+  bool mNeedToReportActiveAfterLoadingBecomesActive : 1;
 };
 
 inline nsISupports* ToSupports(nsDocShell* aDocShell) {