Remove viewport from GrGLRenderTarget.

Change-Id: Id69d8dbe60a38dda2c4c14b02ddeebf230f9299a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/215522
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
6 files changed