Bug 1597499 - Make Session Restore work in Fission, r=nika

Differential Revision: https://phabricator.services.mozilla.com/D107883

docshell/base/BrowsingContext.cpp

@@ -2683,8 +2683,8 @@ bool BrowsingContext::LegacyCheckOnlyOwningProcessCanSet(
   return true;
 }
 
-auto BrowsingContext::LegacyRevertIfNotOwningOrParentProcess(ContentParent* aSource)
-    -> CanSetResult {
+auto BrowsingContext::LegacyRevertIfNotOwningOrParentProcess(
+    ContentParent* aSource) -> CanSetResult {
   if (aSource) {
     MOZ_ASSERT(XRE_IsParentProcess());
 
@@ -3168,6 +3168,11 @@ bool BrowsingContext::CanSet(FieldIndex<IDX_PendingInitialization>,
   return IsTop() && GetPendingInitialization() && !aNewValue;
 }
 
+bool BrowsingContext::CanSet(FieldIndex<IDX_HasRestoreData>, bool aNewValue,
+                             ContentParent* aSource) {
+  return IsTop();
+}
+
 bool BrowsingContext::IsPopupAllowed() {
   for (auto* context = GetCurrentWindowContext(); context;
        context = context->GetParentWindowContext()) {