How to use the @angular/material/core.MatOption.countGroupLabelsBeforeOption function in @angular/material

_scrollToOption() {
        const /** @type {?} */ activeOptionIndex = this.autocomplete._keyManager.activeItemIndex || 0;
        const /** @type {?} */ labelCount = MatOption.countGroupLabelsBeforeOption(activeOptionIndex, this.autocomplete.options, this.autocomplete.optionGroups);
        const /** @type {?} */ optionOffset = (activeOptionIndex + labelCount) * AUTOCOMPLETE_OPTION_HEIGHT;
        const /** @type {?} */ panelTop = this.autocomplete._getScrollTop();
        if (optionOffset < panelTop) {
            // Scroll up to reveal selected option scrolled above the panel top
            this.autocomplete._setScrollTop(optionOffset);
        }
        else if (optionOffset + AUTOCOMPLETE_OPTION_HEIGHT > panelTop + AUTOCOMPLETE_PANEL_HEIGHT) {
            // Scroll down to reveal selected option scrolled below the panel bottom
            const /** @type {?} */ newScrollTop = optionOffset - AUTOCOMPLETE_PANEL_HEIGHT + AUTOCOMPLETE_OPTION_HEIGHT;
            this.autocomplete._setScrollTop(Math.max(0, newScrollTop));
        }
    }
    /**

_calculateOverlayPosition() {
        const /** @type {?} */ itemHeight = this._getItemHeight();
        const /** @type {?} */ items = this._getItemCount();
        const /** @type {?} */ panelHeight = Math.min(items * itemHeight, SELECT_PANEL_MAX_HEIGHT);
        const /** @type {?} */ scrollContainerHeight = items * itemHeight;
        // The farthest the panel can be scrolled before it hits the bottom
        const /** @type {?} */ maxScroll = scrollContainerHeight - panelHeight;
        // If no value is selected we open the popup to the first item.
        let /** @type {?} */ selectedOptionOffset = this.empty ? 0 : /** @type {?} */ ((this._getOptionIndex(this._selectionModel.selected[0])));
        selectedOptionOffset += MatOption.countGroupLabelsBeforeOption(selectedOptionOffset, this.options, this.optionGroups);
        // We must maintain a scroll buffer so the selected option will be scrolled to the
        // center of the overlay panel rather than the top.
        const /** @type {?} */ scrollBuffer = panelHeight / 2;
        this._scrollTop = this._calculateOverlayScroll(selectedOptionOffset, scrollBuffer, maxScroll);
        this._offsetY = this._calculateOverlayOffsetY(selectedOptionOffset, scrollBuffer, maxScroll);
        this._checkOverlayWithinViewport(maxScroll);
    }
    /**

function () {
        var /** @type {?} */ activeOptionIndex = this.autocomplete._keyManager.activeItemIndex || 0;
        var /** @type {?} */ labelCount = MatOption.countGroupLabelsBeforeOption(activeOptionIndex, this.autocomplete.options, this.autocomplete.optionGroups);
        var /** @type {?} */ optionOffset = (activeOptionIndex + labelCount) * AUTOCOMPLETE_OPTION_HEIGHT;
        var /** @type {?} */ panelTop = this.autocomplete._getScrollTop();
        if (optionOffset < panelTop) {
            // Scroll up to reveal selected option scrolled above the panel top
            this.autocomplete._setScrollTop(optionOffset);
        }
        else if (optionOffset + AUTOCOMPLETE_OPTION_HEIGHT > panelTop + AUTOCOMPLETE_PANEL_HEIGHT) {
            // Scroll down to reveal selected option scrolled below the panel bottom
            var /** @type {?} */ newScrollTop = optionOffset - AUTOCOMPLETE_PANEL_HEIGHT + AUTOCOMPLETE_OPTION_HEIGHT;
            this.autocomplete._setScrollTop(Math.max(0, newScrollTop));
        }
    };
    /**

function () {
        var /** @type {?} */ itemHeight = this._getItemHeight();
        var /** @type {?} */ items = this._getItemCount();
        var /** @type {?} */ panelHeight = Math.min(items * itemHeight, SELECT_PANEL_MAX_HEIGHT);
        var /** @type {?} */ scrollContainerHeight = items * itemHeight;
        // The farthest the panel can be scrolled before it hits the bottom
        var /** @type {?} */ maxScroll = scrollContainerHeight - panelHeight;
        // If no value is selected we open the popup to the first item.
        var /** @type {?} */ selectedOptionOffset = this.empty ? 0 : /** @type {?} */ ((this._getOptionIndex(this._selectionModel.selected[0])));
        selectedOptionOffset += MatOption.countGroupLabelsBeforeOption(selectedOptionOffset, this.options, this.optionGroups);
        // We must maintain a scroll buffer so the selected option will be scrolled to the
        // center of the overlay panel rather than the top.
        var /** @type {?} */ scrollBuffer = panelHeight / 2;
        this._scrollTop = this._calculateOverlayScroll(selectedOptionOffset, scrollBuffer, maxScroll);
        this._offsetY = this._calculateOverlayOffsetY(selectedOptionOffset, scrollBuffer, maxScroll);
        this._checkOverlayWithinViewport(maxScroll);
    };
    /**

_scrollActiveOptionIntoView() {
        const /** @type {?} */ itemHeight = this._getItemHeight();
        const /** @type {?} */ activeOptionIndex = this._keyManager.activeItemIndex || 0;
        const /** @type {?} */ labelCount = MatOption.countGroupLabelsBeforeOption(activeOptionIndex, this.options, this.optionGroups);
        const /** @type {?} */ scrollOffset = (activeOptionIndex + labelCount) * itemHeight;
        const /** @type {?} */ panelTop = this.panel.nativeElement.scrollTop;
        if (scrollOffset < panelTop) {
            this.panel.nativeElement.scrollTop = scrollOffset;
        }
        else if (scrollOffset + itemHeight > panelTop + SELECT_PANEL_MAX_HEIGHT) {
            this.panel.nativeElement.scrollTop =
                Math.max(0, scrollOffset - SELECT_PANEL_MAX_HEIGHT + itemHeight);
        }
    }
    /**