[fiddle] Init gpu using the GLTestContext.

The previous way was failing with SwiftShader.

Bug: skia:
Change-Id: I6f3937d4d3bc36851476e29be891dc0a38871ef0
Reviewed-on: https://skia-review.googlesource.com/130325
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
5 files changed