Fix infinite recursion crash in HarfBuzz' CoreText backend
The font cascade reconfiguration which was introduced as fix for AAT
shaping performance regressions in crbug.com/547912 seems to
occasionally cause CoreText crashes on OS X 10.9. We don't have a better
way of detecting this than by OS or CoreText API version number. This is
one of our top Mac crashers on Mac OS 10.9 with Chrome across versions .
This crash does not occur in newer versions of OS X and we can keep this
important performance optimization enabled there.
A big thanks to Robert Sesek (rsesek@) for the patient and thorough
initial investigation. Discussing and working together on this issue we
were able to identify the crash triggering code in HarfBuzz in this