Bug 1673617 - Create BrowsingContext::mChildSessionHistory more aggressively, r=nika

Differential Revision: https://phabricator.services.mozilla.com/D100348

dom/base/nsFrameLoader.cpp

@@ -2519,6 +2519,10 @@ bool nsFrameLoader::TryRemoteBrowserInternal() {
     return false;
   }
 
+  if (mPendingBrowsingContext->IsTop()) {
+    mPendingBrowsingContext->InitSessionHistory();
+  }
+
   // <iframe mozbrowser> gets to skip these checks.
   // iframes for JS plugins also get to skip these checks. We control the URL
   // that gets loaded, but the load is triggered from the document containing

toolkit/components/browser/nsWebBrowser.cpp

@@ -147,10 +147,6 @@ already_AddRefed<nsWebBrowser> nsWebBrowser::Create(
   // handler that always gets called (even for subframes) for any bubbling
   // event.
 
-  if (aBrowsingContext->IsTop()) {
-    aBrowsingContext->InitSessionHistory();
-  }
-
   nsresult rv = docShell->InitWindow(nullptr, docShellParentWidget, 0, 0, 0, 0);
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return nullptr;