The call stack for one of our top crashes looks like this:
```
node::Abort (node_errors.cc:241)
node::Assert (node_errors.cc:256)
node::MakeCallback (callback.cc:226)
gin_helper::internal::CallMethodWithArgs (event_emitter_caller.cc:23)
gin_helper::EmitEvent<T> (event_emitter_caller.h:51)
gin_helper::EventEmitterMixin<T>::Emit<T> (event_emitter_mixin.h:81)
electron::api::DownloadItem::OnDownloadUpdated (electron_api_download_item.cc:115)
download::DownloadItemImpl::UpdateObservers (download_item_impl.cc:482)
content::DownloadManagerImpl::Shutdown (download_manager_impl.cc:508)
content::BrowserContext::~BrowserContext (browser_context.cc:476)
```
Full stack here: https://sentry.io/share/issue/9b030a0601b547188181b543c16ecda2/
During browser shutdown, the `DownloadManager` was being cleaned up
*after* the Node environment had already been destroyed. This caused the
`DownloadItem::OnDownloadUpdated` callback to crash when trying to emit
the JS `done` event.
To prevent this, we now manually shut down the `DownloadManager`
earlier. This is also mentioned in the comment on
`DownloadManager::Shutdown`:
```
// Shutdown the download manager. Content calls this when BrowserContext is
// being destructed. If the embedder needs this to be called earlier, it can
// call it. In that case, the delegate's Shutdown() method will only be called
// once.
```
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