Add 2 fuzz targets for image decoding (oss-fuzz)

This also adds in a few small guards to prevent libfuzzer from frequently
running out of memory when an image claims to have billions of pixels.

Bug: skia:
Change-Id: I47a9daac832c4d85a42000698482b61721c38880
Reviewed-on: https://skia-review.googlesource.com/106264
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
7 files changed