Draws an arc for the favicon status, relative to the total number of tests.
function drawFaviconArc(context, total, start, length, color) {
    var arcStart = ARC_OFFSET + Math.PI * 2 * (start / total);
    var arcEnd = ARC_OFFSET + Math.PI * 2 * ((start + length) / total);
    context.beginPath();
    context.strokeStyle = color;
    context.lineWidth = ARC_WIDTH;
    context.arc(16, 16, 16 - ARC_WIDTH / 2, arcStart, arcEnd);
    context.stroke();
}