src/vs/workbench/services/themes/common/themeExtensionPoints.ts/ThemeRegistry/constructor
class ThemeRegistry:	constructor(
		private readonly themesExtPoint: IExtensionPoint<IThemeExtensionPoint[]>,
		private create: (theme: IThemeExtensionPoint, themeLocation: URI, extensionData: ExtensionData) => T,
		private idRequired = false,
		private builtInTheme: T | undefined = undefined
	) {
		this.extensionThemes = [];
		this.initialize();
	}