Fix GrGLGpu::createTestingOnlyBackendRenderTarget()

The format field wasn't being set.

Make GrContext_colorTypeSupportedAsSurface test that surfaces can be
created from GrBackendRenderTargets.

Change-Id: Ib5ae4671faa3f44102c6436593c7a987a05b3b88
Reviewed-on: https://skia-review.googlesource.com/150134
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
4 files changed