Move calls to conversion_possible to SkCodec

Move common code into the base class, so subclasses need not call
conversion_possible.

Use SkEncodedInfo rather than SkImageInfo, and use the proper frame.

API Changes:
- SkAndroidCodec:
  - Add getEncodedInfo(), for SkBitmapRegionCodec
- SkEncodedInfo:
  - Add opaque() helper
- SkBitmapRegionDecoder:
  - Remove unused conversionSupported

(Split off from skia-review.googlesource.com/c/25746)

Bug: skia:5601
Change-Id: If4a40d4b98a3dd0afde2b6058f92315a393a5baf
Reviewed-on: https://skia-review.googlesource.com/34361
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
21 files changed