Add flag to avoid stencil buffers in Skia

Add flag to avoid stencil buffers in Skia

Certain systems experience a leak in the GL driver associated with
stencil buffers. Attempts to avoid the leak (while still using stencil
buffers) dind't succeed. This patch adds a GrContextOption
fAvoidStencilBuffers. This disables certain path rendering modes, as
well as stencil based masking/clipping.
NOTREECHECKS=true
NOTRY=true
NOPRESUBMIT=true
Bug: 713854
Change-Id: Ifa6c0f2bd5ee395547bda9165d6c79d197ae8b8b
Reviewed-On: https://skia-review.googlesource.com/15253
Commit-Queue: Eric Karl <ericrk@chromium.org>
Reviewed-By: Eric Karl <ericrk@chromium.org>
Reviewed-By: Brian Salomon <bsalomon@google.com>
Reviewed-on: https://skia-review.googlesource.com/17081
Commit-Queue: Eric Karl <ericrk@google.com>