Expand GrGLGpu::flushViewport

and update GrGLGpu::flushScissorRect's signature to match it.

Change-Id: I9082003934168306833f86d310b942a8d7527384
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/350612
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed