* refactor: use base::flat_map in ElectronMenuModel
* refactor: use base::flat_map in BuildSubmenuFromModel()
* refactor: use base::flat_map in GetDialogsMap()
* refactor: use base::flat_map in DesktopCapturer
* refactor: use base::flat_map, flat_set in ElectronBrowserClient
* refactor: use base::flat_map in ProxyingURLLoaderFactory
* refactor: use base::flat_map in MapToCommonId()
* refactor: use base::flat_map for g_map_id
* refactor: use base::flat_map for ViewsDelegate::AppbarAutohideEdgeMap
* refactor: use base::flat_map for App::app_metrics_
* refactor: use base::flat_map for PowerSaveBlocker::wake_lock_types_
* refactor: use base::flat_map for NativeImage::hicons_
* refactor: use base::flat_map for MenuViews::menu_runners_
* refactor: use base::flat_map for WebViewManager::web_contents_embedder_map_
* refactor: use base::flat_map for InspectableWebContents::extensions_api_
* refactor: use base::flat_set for libnotify GetServerCapabilities()
* refactor: use base::flat_set for InspectableWebContents::loaders_
* refactor: use base::flat_set for ElectronRendererClient::environments_
refactor: use base::flat_set for ElectronRendererClient::injected_frames_
* refactor: use base::flat_set for WebWorkerObserver::environments_
