Improve comments describing common sRGB curves
Improve comments describing common sRGB curves

BUG=skia:5897

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4037

Change-Id: Id1253cc9b960aad47bc0f9b7e40f10830d46d98d
Reviewed-on: https://skia-review.googlesource.com/4037
Reviewed-by: Heather Miller <2e22000c5d22374561fe5fba576a31095b72dc2e@google.com>
Commit-Queue: Matt Sarett <bb43c9b8214fcf1292f134c9714ba8a0e7075913@google.com>

Hikari-no-Tenshi/android_external_skia,rubenvb/skia,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,rubenvb/skia,google/skia,rubenvb/skia,google/skia,rubenvb/skia,google/skia,HalCanary/skia-hc,rubenvb/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,google/skia,google/skia,google/skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,google/skia