src/vs/workbench/contrib/mergeEditor/browser/view/mergeEditor.ts/MergeEditor/toggleShowBaseTop
class MergeEditor:	public toggleShowBaseTop(): void {
		const showBaseTop = this._layoutMode.value.showBase && this._layoutMode.value.showBaseAtTop;
		this.setLayout({
			...this._layoutMode.value,
			showBaseAtTop: true,
			showBase: !showBaseTop,
		});
	}