Reland "Add small offset to t in GrLinearGradientLayout."

[cherry-pick of 6b2ccfcf6730c1d4fb879b9726a6f33d3e6f38f8 from
skia/master]
[cherry-pick of b0fae436b91950935035f6e5bbe02495af92a830 from
skqp/release]

Original change's description:
> Revert "Add small offset to t in GrLinearGradientLayout."
>
> This reverts commit 1a15723397a069c07705f8ed4f9f4c9a0c194816.
>
> Reason for revert: causes two layout tests to "fail". Need to disable tests
>
> Original change's description:
> > Add small offset to t in GrLinearGradientLayout.
> >
> > This works around a varying interpolation issue when a hard stop occurs
> > a along a row or column of pixel centers.
> >
> > Bug: chromium:938592
> > Change-Id: I4c239b2831c3e901cbbfa43f0a60a3d7fb0fef75
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/200939
> > Reviewed-by: Michael Ludwig <michaelludwig@google.com>
> > Commit-Queue: Brian Salomon <bsalomon@google.com>
>
> TBR=bsalomon@google.com,michaelludwig@google.com
>
> Change-Id: Iebe45929050b8ab1d07574518a1b3d9ac5147512
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: chromium:938592
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201655
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>

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

Bug: 144257628
Change-Id: Ibd35a39d788d74752ccf2a8ffbac8009928540c7
Reviewed-On: https://skia-review.googlesource.com/c/skia/+/201617
Reviewed-By: Brian Salomon <bsalomon@google.com>
Reviewed-By: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271741
Reviewed-by: Tyler Denniston <tdenniston@google.com>
Test: CtsSkQPTestCases
2 files changed