Glide3.7 添加 Webp支持

问题：项目加载webp图片不显示
背景：后台的图片从png转为了webp，出现部分图片不能显示。
原因：项目使用的glide 3.7 不支持带透明效果的webp格式图片
对策：
1.使用最新的glide 4.7.1。由于相比 glide 3.7 API改动太大，需要修改很多文件，比较麻烦。
2.修改glide 3.7 源码：按照4.7.1的代码，增加webp支持，重新打包。
以下是修改方法：

文件：com\bumptech\glide\load\resource\bitmap\ImageHeaderParser.java
加入枚举值WEBP 和WEBPA ,gettype() 方法加入webp解析 相关字段

    public enum ImageType {
        /** GIF type. */
        GIF(true),
        /** JPG type. */
        JPEG(false),
        /** PNG type with alpha. */
        PNG_A(true),
        /** PNG type without alpha. */
        PNG(false),
        /** WebP type with alpha. */
        WEBP_A(true),
        /** WebP type without alpha. */
        WEBP(false),
        /** Unrecognized type. */
        UNKNOWN(false);
        private final boolean hasAlpha;

        ImageType(boolean hasAlpha) {
            this.hasAlpha = hasAlpha;
        }

        public boolean hasAlpha() {
            return hasAlpha;
        }
    }

    //copy from glide 4.7.1
    // WebP-related
    // "RIFF"
    private static final int RIFF_HEADER = 0x52494646;
    // "WEBP"
    private static final int WEBP_HEADER = 0x57454250;
    // "VP8" null.
    private static final int VP8_HEADER = 0x56503800;
    private static final int VP8_HEADER_MASK = 0xFFFFFF00;
    private static final int VP8_HEADER_TYPE_MASK = 0x000000FF;
    // 'X'
    private static final int VP8_HEADER_TYPE_EXTENDED = 0x00000058;
    // 'L'
    private static final int VP8_HEADER_TYPE_LOSSLESS = 0x0000004C;
    private static final int WEBP_EXTENDED_ALPHA_FLAG = 1 << 4;
    private static final int WEBP_LOSSLESS_ALPHA_FLAG = 1 << 3;


    public ImageType getType() throws IOException {
        final int firstTwoBytes = streamReader.getUInt16();

        // JPEG.
        if (firstTwoBytes == EXIF_MAGIC_NUMBER) {
            return JPEG;
        }

        final int firstFourBytes = (firstTwoBytes << 16 & 0xFFFF0000) | (streamReader.getUInt16() & 0xFFFF);
        // PNG.
        if (firstFourBytes == PNG_HEADER) {
            // See: http://stackoverflow.com/questions/2057923/how-to-check-a-png-for-grayscale-alpha
            // -color-type
            streamReader.skip(25 - 4);
            int alpha = streamReader.getByte();
            // A RGB indexed PNG can also have transparency. Better safe than sorry!
            return alpha >= 3 ? PNG_A : PNG;
        }

        // GIF from first 3 bytes.
        if (firstFourBytes >> 8 == GIF_HEADER) {
            return GIF;
        }

        // WebP (reads up to 21 bytes). See https://developers.google.com/speed/webp/docs/riff_container
        // for details.
        if (firstFourBytes != RIFF_HEADER) {
            return UNKNOWN;
        }
        // Bytes 4 - 7 contain length information. Skip these.
        streamReader.skip(4);
        final int thirdFourBytes =
                (streamReader.getUInt16() << 16 & 0xFFFF0000) | (streamReader.getUInt16() & 0xFFFF);
        if (thirdFourBytes != WEBP_HEADER) {
            return UNKNOWN;
        }
        final int fourthFourBytes =
                (streamReader.getUInt16() << 16 & 0xFFFF0000) | (streamReader.getUInt16() & 0xFFFF);
        if ((fourthFourBytes & VP8_HEADER_MASK) != VP8_HEADER) {
            return UNKNOWN;
        }
        if ((fourthFourBytes & VP8_HEADER_TYPE_MASK) == VP8_HEADER_TYPE_EXTENDED) {
            // Skip some more length bytes and check for transparency/alpha flag.
            streamReader.skip(4);
            return (streamReader.getByte() & WEBP_EXTENDED_ALPHA_FLAG) != 0 ? ImageType.WEBP_A : ImageType.WEBP;
        }
        if ((fourthFourBytes & VP8_HEADER_TYPE_MASK) == VP8_HEADER_TYPE_LOSSLESS) {
            // See chromium.googlesource.com/webm/libwebp/+/master/doc/webp-lossless-bitstream-spec.txt
            // for more info.
            streamReader.skip(4);
            return (streamReader.getByte() & WEBP_LOSSLESS_ALPHA_FLAG) != 0 ? ImageType.WEBP_A : ImageType.WEBP;
        }
        return ImageType.WEBP;
    }

文件：com\bumptech\glide\load\resource\bitmap\Downsampler.java
TYPES_THAT_USE_POOL 集合内加入WEBP 和WEBPA

    private static final Set<ImageHeaderParser.ImageType> TYPES_THAT_USE_POOL = EnumSet.of(
            ImageHeaderParser.ImageType.JPEG, ImageHeaderParser.ImageType.PNG_A, ImageHeaderParser.ImageType.PNG, ImageHeaderParser.ImageType.WEBP, ImageHeaderParser.ImageType.WEBP_A); 

重新打包文件下载：https://download.youkuaiyun.com/download/u011809807/10498207