function premultiplyTint(tint, alpha) {
    if (alpha === 1.0) {
        return (alpha * 255 << 24) + tint;
    }
    if (alpha === 0.0) {
        return 0;
    }
    var R = ((tint >> 16) & 0xFF);
    var G = ((tint >> 8) & 0xFF);
    var B = (tint & 0xFF);
    R = ((R * alpha) + 0.5) | 0;
    G = ((G * alpha) + 0.5) | 0;
    B = ((B * alpha) + 0.5) | 0;
    return (alpha * 255 << 24) + (R << 16) + (G << 8) + B;
}
premultiplies tint
@memberof PIXI.utils
@function premultiplyTint
@param {number} tint - integer RGB
@param {number} alpha - floating point alpha (0.0-1.0)
@returns {number} tint multiplied by alpha