src/vs/workbench/api/common/extHostTimeline.ts/ExtHostTimeline/constructor
class ExtHostTimeline:	constructor(
		mainContext: IMainContext,
		commands: ExtHostCommands,
	) {
		this._proxy = mainContext.getProxy(MainContext.MainThreadTimeline);

		commands.registerArgumentProcessor({
			processArgument: arg => {
				if (arg && arg.$mid === MarshalledId.TimelineActionContext) {
					const uri = arg.uri === undefined ? undefined : URI.revive(arg.uri);
					return this._itemsBySourceAndUriMap.get(arg.source)?.get(getUriKey(uri))?.get(arg.handle);
				}

				return arg;
			}
		});
	}