Add animation support to SkWebpCodec

TBR=reed@google.com
(No change to the public API, but changed a header file)

SkWebpCodec:
- Implement onGetFrameCount, onGetFrameInfo, and onGetRepetitionCount
- Respect the alpha reported by libwebp. Although the spec states that
  it is only a hint, the libwebp encoder uses it properly. Respecting
  allows us to draw opaque images faster and decode them to 565. This
  also matches other SkCodecs (and Chromium).
- onGetPixels:
  - Decode the frame requested, recursively decoding required frame if
    necessary
  - When blending with a prior frame, use SkRasterPipeline

SkCodec:
- Move check for negative index to getFrameInfo
- Reset the colorXform if one is not needed

SkCodecAnimation:
- Add new blend enum, for WebP's (and APNG's) non-blending option

SkFrameHolder:
- New base classes for frames and the owner of the frames, allowing
  code sharing between SkWebpCodec and SkGifCodec (particularly for
  determining whether a frame has alpha and what frame it depends on)
- When moving items from SkGIFFrameContext, use Skia conventions (i.e.
  int instead of unsigned)
- Rename "delay time" to "duration", to match e.g. SkFrameInfo::
  fDuration

SkGifImageReader:
- Move pieces to SkFrameHolder, and adapt to changes made in the
  process
- Make setAlphaAndRequiredFrame (now on the base class SkFrameHolder)
  more general to support webp, and add support for frames that do not
  blend
- Change SkGIFFrameContext from a struct to a class, to match how we
  use the distinction elsewhere (i.e. struct is a small object with
  public fields)
- Rework hasTransparentPixel (now hasTransparency, since it returns true
  in some cases where there is not a transparent pixel) to better fit
  with the modified setAlphaAndRequiredFrame. Also be more consistent
  when there is no transparent pixel but no color map.
- Simplify an if condition that was previously simplified in 2d61e717
  but accidentally got reverted in a4db9be6

CodecAnimTest:
- Test new animated webp files
- Rearrange the test to more cleanly print alpha type mismatches for
  the first frame

resources:
- webp-animated.webp
  - animated webp from Chromium
- blendBG.webp
  - new webp file using bits of webp-animated-semitransparent4.webp
    from Chromium
  - tests required frame and alpha when using the non-blending mode
  - frames have the following properties:
    - Frame 0: no alpha, fills screen
    - Frame 1: alpha, fills screen
    - Frame 2: no alpha, fills screen
    - Frame 3: alpha, fills screen, blendBG
    - Frame 4: no alpha, fills screen, blendBG
    - Frame 5: alpha, blendBG
    - Frame 6: covers 4, has alpha, blendBG
  - also used to test decoding to 565 if the new frame data has alpha
    but blends onto an opaque frame

DM.cpp:
- Test animated images to non-native 8888 and unpremul

DMSrcSink.cpp:
- Do not test non-native 8888 decodes to f16 dst
- Test unpremul decodes to f16
- Copy a frame of an animated image prior to drawing, since in unpremul
  mode, the DM code will premultiply first.

Bug: skia: 3315
Change-Id: I4e55ae2ee5bc095b37a743bdcfac644be603b980
Reviewed-on: https://skia-review.googlesource.com/16707
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
2 files changed