Add glPolygonMode support.

Mainly added because it's useful for rendering in wireframe mode.

Change-Id: I84dab43ce5b56a48d47dd16d4c98fa7648bb1f0b
Reviewed-on: https://skia-review.googlesource.com/10530
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
8 files changed