extensions/markdown-language-features/src/preview/preview.ts/MarkdownPreview/refresh
class MarkdownPreview:	public refresh(forceUpdate: boolean = false) {
		// Schedule update if none is pending
		if (!this.throttleTimer) {
			if (this.firstUpdate) {
				this.updatePreview(true);
			} else {
				this.throttleTimer = setTimeout(() => this.updatePreview(forceUpdate), this.delay);
			}
		}

		this.firstUpdate = false;
	}