Store mipmap levels in deferred texture image

Store mipmap levels in deferred texture image

This is a follow-up to https://codereview.chromium.org/2034933003/ which
was reverted due to a memory leak.

When creating the deferred texture image, detect if using medium / high
quality. If so, generate and store mipmaps in the deferred texture
image.

When creating a texture from that be sure to read it back out.

BUG=578304
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2115023002

Review-Url: https://codereview.chromium.org/2115023002