Replace SkSpecialImage::makeTightSubset with asImage (take 2)

This is a reland of https://skia-review.googlesource.com/c/8498/ (Replace SkSpecialImage::makeTightSubset with asImage)

It must wait on https://codereview.chromium.org/2702703002/ (Add suppressions for upcoming Skia DEPS roll) due to minor layout test changes

This should allow the relanding of:

https://skia-review.googlesource.com/c/8450/ (Remove asTextureRef from SkSpecialImage & update effects accordingly (take 2))

Change-Id: I7086a419869dbeb62d9b9e9714c796d54e75ee49
Reviewed-on: https://skia-review.googlesource.com/8701
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed