src/vs/editor/browser/viewParts/marginDecorations/marginDecorations.ts/MarginViewLineDecorationsOverlay/_getDecorations
class MarginViewLineDecorationsOverlay:	protected _getDecorations(ctx: RenderingContext): DecorationToRender[] {
		const decorations = ctx.getDecorationsInViewport();
		const r: DecorationToRender[] = [];
		let rLen = 0;
		for (let i = 0, len = decorations.length; i < len; i++) {
			const d = decorations[i];
			const marginClassName = d.options.marginClassName;
			if (marginClassName) {
				r[rLen++] = new DecorationToRender(d.range.startLineNumber, d.range.endLineNumber, marginClassName);
			}
		}
		return r;
	}