public int getFrameCount() {
    if (!mDecoded) {
      throw new IllegalStateException("getFrameCount called before decode");
    }
    return mFrameControls.size();
  }
@param is InputStream to decode
@param os OutputStream to write fixed version of gif, if needed. (optional)
animated-gif-lite/src/main/java/com/facebook/animated/giflite/decoder/GifMetadataDecoder.java