* perf: use an absl::flat_hash_set for UsbChooserContext::ephemeral_devices_
* perf: use an absl::flat_hash_set for GlobalMenuBarRegistrarX11::live_windows_
* perf: use an absl::flat_hash_set for NativeWindowViews::forwarding_windows_
* perf: use an absl::flat_hash_set for OffScreenRenderWidgetHostView::guest_host_views_
perf: use an absl::flat_hash_set for OffScreenRenderWidgetHostView::proxy_views_
* perf: use an absl::flat_hash_set for NativeWindow::injected_frames_
* perf: use an absl::flat_hash_set for NativeWindow::background_throttling_sources_
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