Remove reference to SkImageDecoder from SkPicture. Make the default
InstallPixelRefProc passed to CreateFromStream use
SkImageGenerator::NewFromEncoded instead.
Make SkImageGenerator::NewFromEncoded create an SkCodecImageGenerator.
Remove the old version that used SkImageDecoder.
Remove all versions of lazy_decode_bitmap/LazyDecodeBitmap. The default
now behaves lazily.
Update all clients to use the default.
Move SkImageDecoderGenerator into KtxTest.cpp, and use it directly.
BUG=skia:4691
BUG=skia:4290
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Review URL: https://codereview.chromium.org/1671193002