public AnimatedImageResultBuilder setFrameForPreview(int frameForPreview) {
    mFrameForPreview = frameForPreview;
    return this;
  }
Sets the frame that should be used for the preview image. If the preview bitmap was fetched,
this is the frame that it's for.

@return the frame that should be used for the preview image
animated-base/src/main/java/com/facebook/imagepipeline/animated/base/AnimatedImageResultBuilder.java