src/vs/workbench/contrib/welcomeGettingStarted/browser/gettingStartedService.ts/WalkthroughsService/progressStep
class WalkthroughsService:	progressStep(id: string) {
		const oldProgress = this.stepProgress[id];
		if (!oldProgress || oldProgress.done !== true) {
			this.stepProgress[id] = { done: true };
			this.memento.saveMemento();
			const step = this.getStep(id);
			if (!step) { throw Error('Tried to progress unknown step'); }

			this._onDidProgressStep.fire(this.getStepProgress(step));
		}
	}