Starting a "width" transition for a simple <div> will return the same values for "from" and "to" when getKeyframes() is called. This cannot be correct since a transition cannot have the same from and to values. Digging into this, this is about this code in ComputedStyleExtractor::valueForPropertyInStyle():

        case CSSPropertyWidth:
            if (renderer && !renderer->isRenderOrLegacyRenderSVGModelObject()) {
                // According to http://www.w3.org/TR/CSS2/visudet.html#the-width-property,
                // the "width" property does not apply for non-replaced inline elements.
                if (!isNonReplacedInline(*renderer))
                    return zoomAdjustedPixelValue(sizingBox(*renderer).width(), style);
            }
            return zoomAdjustedPixelValueForLength(style.width(), style);

In this case we end up calling zoomAdjustedPixelValue(sizingBox(*renderer).width(), style) which simply does not use the values provided in the RenderStyle for the keyframe.