src/vs/workbench/browser/parts/editor/editorPart.ts/EditorPart/setGroupOrientation
class EditorPart:	setGroupOrientation(orientation: GroupOrientation): void {
		if (!this.gridWidget) {
			return; // we have not been created yet
		}

		const newOrientation = (orientation === GroupOrientation.HORIZONTAL) ? Orientation.HORIZONTAL : Orientation.VERTICAL;
		if (this.gridWidget.orientation !== newOrientation) {
			this.gridWidget.orientation = newOrientation;
		}
	}