Fix drawing SkAnimatedImages with transparency

Bug: b/74195953

Do not use SkBlendMode::kSrc, which overwrites the pixels that were
already present. Instead, blend normally.

Change-Id: Ie6843c6278212fddddd0ba0ae292fdb5eaf2342e
Reviewed-on: https://skia-review.googlesource.com/112200
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Leon Scroggins <scroggo@google.com>
2 files changed