Create mipped texture proxys for PictureImageGenerator

Bug: skia:
Change-Id: If86b01e5c008537de8c9af99000559bf524c836f
Reviewed-on: https://skia-review.googlesource.com/63260
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
2 files changed