src/vs/editor/common/viewModel/viewModelImpl.ts/ViewModel/setViewport
class ViewModel:	public setViewport(startLineNumber: number, endLineNumber: number, centeredLineNumber: number): void {
		this._viewportStartLine = startLineNumber;
		const position = this.coordinatesConverter.convertViewPositionToModelPosition(new Position(startLineNumber, this.getLineMinColumn(startLineNumber)));
		this._viewportStartLineTrackedRange = this.model._setTrackedRange(this._viewportStartLineTrackedRange, new Range(position.lineNumber, position.column, position.lineNumber, position.column), TrackedRangeStickiness.NeverGrowsWhenTypingAtEdges);
		const viewportStartLineTop = this.viewLayout.getVerticalOffsetForLineNumber(startLineNumber);
		const scrollTop = this.viewLayout.getCurrentScrollTop();
		this._viewportStartLineDelta = scrollTop - viewportStartLineTop;
	}