src/vs/editor/common/viewModel/viewModelImpl.ts/ViewModel/_captureStableViewport
class ViewModel:	private _captureStableViewport(): StableViewport {
		// We might need to restore the current start view range, so save it (if available)
		// But only if the scroll position is not at the top of the file
		if (this._viewportStart.isValid && this.viewLayout.getCurrentScrollTop() > 0) {
			const previousViewportStartViewPosition = new Position(this._viewportStart.viewLineNumber, this.getLineMinColumn(this._viewportStart.viewLineNumber));
			const previousViewportStartModelPosition = this.coordinatesConverter.convertViewPositionToModelPosition(previousViewportStartViewPosition);
			return new StableViewport(previousViewportStartModelPosition, this._viewportStart.startLineDelta);
		}
		return new StableViewport(null, 0);
	}