***Turns on color correct rendering for Android and iOS
***Communicates dst color space to raster cache
***Turns on color space aware image decoding

Test:
***color_testing_demo on Pixel XL
***flutter_gallery on iPad Mini and iPad Pro (haven't figured out how to run manual_tests on iOS)

TODO:
I needed to split up this CL somewhere. These are follow-up tasks.
***Make desktop backends color correct
***Make debugging tools (ex: encoding frames to png) preserve color space
***Investigate using UIKit API to allow iOS to fine tune color space of rendered content