Assert we are now in the world of single-primitive-type render passes

We want this to be true so that we can know ahead of time what the primitiveType of a given render pass will be and add it to the GrProgramInfo.

This is pulled out of https://skia-review.googlesource.com/c/skia/+/252161/ (Add GrPrimitiveType to GrProgramInfo)

Bug: skia:9455
Change-Id: I3e6365da6db5349dfe7329ef1e20b8c1d6267ff1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/252925
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
3 files changed