Use glXCreateContextAttribsARB in viewer to make it easier to attach RenderDoc.

Change-Id: I0cc82fe826b81a082b579f60af3d9ef35d5fe351
Reviewed-on: https://skia-review.googlesource.com/9407
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed