Support Skia's gray SkColorSpaces

Bug: 153410582
Test: I0a280cdfdb02766f5e415408386cce49a59504ab

For gray color spaces, Skia creates a special toXYZD50 matrix which does
not have any concept of primaries. Update the Java ColorSpace to
recognize such a matrix and treat it specially. Instead of creating
primaries, use a set of dummy values.

This fixes a bug where the Java ColorSpace was invalid (NaNs in its
transforms) and applying it to a new Bitmap yielded incorrect results.

Fix up the @see links in getPrimaries and surrounding methods.

Change-Id: I94fe232e10f56a69832d4a39a2e5909eac641264
(cherry picked from commit d82d585f)
Merged-In: I94fe232e10f56a69832d4a39a2e5909eac641264