Add a basic constructor to GrPipeline

Adds a simple constructor for when we just need to set up basic
internal rendering.

BUG=skia:

Change-Id: Ib046c62e9a759aa7d0a3345e16ccf6e6af9342ea
Reviewed-on: https://skia-review.googlesource.com/8121
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
4 files changed