Revert "move GrColor.h to private, IWYU"

This reverts commit e602f395813aab8242afad356008b8e79911adbb.

Reason for revert: Breaks PDFIUM

Original change's description:
> move GrColor.h to private, IWYU
> 
> Bug: skia:
> Change-Id: I0f0dabd7cc54cb7786f53bd6da0c0c012375037e
> Reviewed-on: https://skia-review.googlesource.com/104160
> Commit-Queue: Mike Reed <reed@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>

TBR=bsalomon@google.com,reed@google.com

Change-Id: Ifaa50f8771fa1ca8bc152270efdb1fe27f7210f2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/104440
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
20 files changed