Revert "Reland: Remove SkLights include from SkCanvas.h"

Revert "Reland: Remove SkLights include from SkCanvas.h"

This reverts commit fed00319c9bafa41c8df658708030c072b301a41.

Reason for revert: breaking the Android roll.

Original change's description:
> Reland: Remove SkLights include from SkCanvas.h
>
> SkLights.h pulls in a bunch of other headers and is not needed (fwdecl
> works fine).
>
> Change-Id: I3ed97cd7861e51dcb7cfa7950a97b420dbc6fbfb
> TBR=reed@google.com
> Reviewed-on: https://skia-review.googlesource.com/15143
> Commit-Queue: Florin Malita <fmalita@chromium.org>
> Reviewed-by: Florin Malita <fmalita@chromium.org>
>

TBR=fmalita@chromium.org,reed@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I3b0e69f1d04d160f16a5567b09982d35cc9ca84e
Reviewed-on: https://skia-review.googlesource.com/15195
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>