When a frame is being closed, GC is triggered in this flow:
 LocalFrame::Detach()
  -> ScriptController::ClearForClose()
   -> WindowProxyManager::ClearForClose()
    -> WindowProxy::ClearForClose()
     -> V8GCForContextDispose::NotifyContextDisposed()
      -> Isolate::ContextDisposedNotification()
       -> Heap::NotifyContextDisposed()
        -> MemoryReducer::NotifyPossibleGarbage()

We should introduce a similar mechanism to trigger GC when finishing service worker install event handler.