subdivide path when side-clipping fails

Please review concept; I'm OK not to check this in.

If the root finder fails, subdivide the curve and try again.
This is complicated by the reversed nature of the curves;
maybe it can be simpler, but how to do that escapes me.

R=reed@google.com
BUG=514246

Review URL: https://codereview.chromium.org/1299243002
2 files changed