src/vs/editor/common/viewLayout/linesLayout.ts/LinesLayout/onLinesDeleted
class LinesLayout:	public onLinesDeleted(fromLineNumber: number, toLineNumber: number): void {
		this._checkPendingChanges();
		fromLineNumber = fromLineNumber | 0;
		toLineNumber = toLineNumber | 0;

		this._lineCount -= (toLineNumber - fromLineNumber + 1);
		for (let i = 0, len = this._arr.length; i < len; i++) {
			const afterLineNumber = this._arr[i].afterLineNumber;

			if (fromLineNumber <= afterLineNumber && afterLineNumber <= toLineNumber) {
				// The line this whitespace was after has been deleted
				//  => move whitespace to before first deleted line
				this._arr[i].afterLineNumber = fromLineNumber - 1;
			} else if (afterLineNumber > toLineNumber) {
				// The line this whitespace was after has been moved up
				//  => move whitespace up
				this._arr[i].afterLineNumber -= (toLineNumber - fromLineNumber + 1);
			}
		}
	}