Bug 1563409: Inherit RemoteSubframes and RemoteTabs flags from parent docshells. r=nika

This also adds an extra assertion against browsing context mismatches that
happen when we don't get this right.

Differential Revision: https://phabricator.services.mozilla.com/D36852

--HG--
extra : source : 4b07deb4cd2ef4c98b6d6ee961a20705f4f2deae

docshell/base/nsDocShell.cpp

@@ -3344,6 +3344,9 @@ nsDocShell::AddChild(nsIDocShellTreeItem* aChild) {
     childDocShell->SetUseGlobalHistory(true);
   }
 
+  Cast(childDocShell)->SetRemoteTabs(mUseRemoteTabs);
+  Cast(childDocShell)->SetRemoteSubframes(mUseRemoteSubframes);
+
   if (aChild->ItemType() != mItemType) {
     return NS_OK;
   }

dom/ipc/WindowGlobalParent.cpp

@@ -333,6 +333,7 @@ already_AddRefed<Promise> WindowGlobalParent::ChangeFrameRemoteness(
         // in-process frame. For remote frames, the BrowserBridgeParent::Init
         // method should've already set up the OwnerProcessId.
         uint64_t childId = browserParent->Manager()->ChildID();
+        MOZ_ASSERT_IF(bridge, browsingContext == browserParent->GetBrowsingContext());
         MOZ_ASSERT_IF(bridge, browsingContext->IsOwnedByProcess(childId));
         browsingContext->SetOwnerProcessId(childId);