Make EGL test context access GL via GrGLInterface

Bug: skia:7334
Change-Id: I5153ef83ae350648a15d6dc427b03d464258608b
Reviewed-on: https://skia-review.googlesource.com/75980
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
9 files changed