Enable tessellating GPU path renderer.

This also contains a fix to remove recursion from the sorted_merge()
step. This was essentially tail-recursion, and was causing stack
exhaustion on some platforms. Making it iterative fixes the issue.

Note: this CL will affect a large number of GPU GM results.

R=bsalomon@google.com
BUG=

Review URL: https://codereview.chromium.org/1080113004
2 files changed