Improve test coverage of image decode modes

Improve test coverage of image decode modes

Summary of the new world...

--image

CodecSrc and ImageGenSrc tests run on:
(1) 8888 with kIgnore transfer fn behavior
(2) srgb with kRespect transfer fn behavior
(3) f16

AndroidCodecSrc and BRDCodecSrc tests run on:
(1) 8888, since SkAndroidCodec always uses kIgnore
(2) f16, since android uses f16

--colorImage

ColorCodecSrc tests run on:
(1) 8888 in kBaseline mode, so we can see what the raw pixels look like
(2) srgb in color correct modes
(3) f16 in color correct modes

Bug: skia:
Change-Id: I65d1a04051da6f94bf5e48f7bc610f482870dc75
Reviewed-on: https://skia-review.googlesource.com/17396
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>