Cleanup and simplify some skiaserve and utility code

This started with a search for gammaCloseToSRGB and turned into me
removing a bunch of really crazy bitmap code here. Like DM, just use
SkPngEncoder to encode PNGs. With that change, we don't need the custom
raster pipeline step, and we can remove that (along with several other
unused functions) from picture_utils. (The one remaining function should
just move to tool_utils, but I'll save that for another rainy day).

In getPixel, we can skip ALL of the processing work, and also only read
the one pixel we need. That makes break-on-change feel much faster from
my anecdotal testing.

Change-Id: I3d18f1e7a15dd12ac4661da1b724e9d8e1cdee96
Reviewed-on: https://skia-review.googlesource.com/146442
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed