src/vs/editor/browser/widget/diffReview.ts/DiffReview/_getPrevRow
class DiffReview:	private _getPrevRow(): HTMLElement {
		const current = this._getCurrentFocusedRow();
		if (!current) {
			return this._getFirstRow();
		}
		if (current.previousElementSibling) {
			return <HTMLElement>current.previousElementSibling;
		}
		return current;
	}