src/vs/editor/browser/widget/diffReview.ts/DiffEntry/getType
class DiffEntry:	public getType(): DiffEntryType {
		if (this.originalLineStart === 0) {
			return DiffEntryType.Insert;
		}
		if (this.modifiedLineStart === 0) {
			return DiffEntryType.Delete;
		}
		return DiffEntryType.Equal;
	}