Bug 1533447 - Part 1: Sync cached browsing contexts to non-owning child processes. r=nika

Differential Revision: https://phabricator.services.mozilla.com/D28668

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

dom/ipc/ContentParent.cpp

@@ -5700,6 +5700,17 @@ mozilla::ipc::IPCResult ContentParent::RecvDetachBrowsingContext(
     aContext->Detach(/* aFromIPC */ true);
   }
 
+  for (auto iter = aContext->Group()->ContentParentsIter(); !iter.Done();
+       iter.Next()) {
+    nsRefPtrHashKey<ContentParent>* entry = iter.Get();
+    if (entry->GetKey() == this) {
+      continue;
+    }
+
+    Unused << entry->GetKey()->SendDetachBrowsingContext(aContext,
+                                                         aMoveToBFCache);
+  }
+
   return IPC_OK();
 }