[gold] mem_diffstore.go: Make ImageHandler read images from the ImageLoader in-memory cache instead of serving them from disk.
[gold] mem_diffstore.go: Make ImageHandler read images from the ImageLoader in-memory cache instead of serving them from disk.

Bug: skia:9356
Change-Id: I3e4ea2dbe2c4b958944bf86f34bf622ef9fa71c1
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/236344
Commit-Queue: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@google.com>
Reviewed-by: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot