Revert "Use std::vector::front()/back() when inserting color stops"

This reverts commit a5851fa3c0dc1ec3303f2cfb4987a4f89ee5d39d.

Reason for revert: Chrome roll failing.

Original change's description:
> Use std::vector::front()/back() when inserting color stops
>
> Follow-up to review comments in [1]. No functional change.
>
> [1] https://skia-review.googlesource.com/c/skia/+/646416
>
> Bug: oss-fuzz:55906
> Cq-Include-Trybots: luci.skia.skia.primary:Test-Android-Clang-GalaxyS20-GPU-MaliG77-arm64-Release-All-Android_NativeFonts
> Change-Id: Ia71ab93784b2fcbcae271b4e28eab57701b126be
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/653696
> Commit-Queue: Dominik Röttsches <drott@chromium.org>
> Commit-Queue: Dominik Röttsches <drott@google.com>
> Reviewed-by: Ben Wagner <bungeman@google.com>

Bug: oss-fuzz:55906
Change-Id: Ie01aa5d37162a6c25e487d98792efe80032838a9
Cq-Include-Trybots: luci.skia.skia.primary:Test-Android-Clang-GalaxyS20-GPU-MaliG77-arm64-Release-All-Android_NativeFonts
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/653917
Auto-Submit: Joe Gregorio <jcgregorio@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
1 file changed