_updateLineWidthsSlowIfDomDidLayout(domReadingContext) {
        if (!domReadingContext.didDomLayout) {
            // only proceed if we just did a layout
            return;
        }
        if (this._asyncUpdateLineWidths.isScheduled()) {
            // reading widths is not scheduled => widths are up-to-date
            return;
        }
        this._asyncUpdateLineWidths.cancel();
        this._updateLineWidthsSlow();
    }
Update the line widths using DOM layout information after someone else
has caused a synchronous layout.