Revert of Remove relative path to GrColor.h in SkShader.h (https://codereview.chromium.org/422023005/)

Reason for revert:
As Ben suspected, this breaks the chrome build.

Original issue's description:
> Remove relative path to GrColor.h in SkShader.h
>
> Committed: https://skia.googlesource.com/skia/+/939f430f660d26e46116a38d2a8436afbd55dfb9

R=bungeman@google.com, george@mozilla.com
TBR=bungeman@google.com, george@mozilla.com
NOTREECHECKS=true
NOTRY=true

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/423943005
2 files changed