8u40 review request: RT-30107 - use fast mask methods for Canvas clipping

[Jim Graham]

Jira: https://javafx-jira.kenai.com/browse/RT-30107
webrev: http://cr.openjdk.java.net/~flar/RT-30107/webrev.00/

Some explanation and benchmark results are in the Jira comments...

                        ...jim