Bug 1542790 - Part 5: Relax toplevel BC requirements, r=qdot

Differential Revision: https://phabricator.services.mozilla.com/D27516

--HG--
extra : moz-landing-system : lando

docshell/base/CanonicalBrowsingContext.cpp

@@ -122,9 +122,6 @@ void CanonicalBrowsingContext::SetEmbedderWindowGlobal(
   if (RefPtr<BrowsingContext> parent = GetParent()) {
     MOZ_RELEASE_ASSERT(aGlobal->BrowsingContext() == parent,
                        "Embedder has incorrect browsing context");
-  } else {
-    MOZ_RELEASE_ASSERT(aGlobal->IsInProcess(),
-                       "Toplevel must have a parent-process embedder");
   }
 
   mEmbedderWindowGlobal = aGlobal;