src/vs/base/common/keybindingLabels.ts/ModifierLabelProvider/constructor
class ModifierLabelProvider:	constructor(mac: ModifierLabels, windows: ModifierLabels, linux: ModifierLabels = windows) {
		this.modifierLabels = [null!]; // index 0 will never me accessed.
		this.modifierLabels[OperatingSystem.Macintosh] = mac;
		this.modifierLabels[OperatingSystem.Windows] = windows;
		this.modifierLabels[OperatingSystem.Linux] = linux;
	}