Implement DTrace hooks for dashcode and instruments.
API/JSProfilerPrivate.cpp: Added. Expose SPI so that profiling can be
turned on from a client. The DTrace probes were added within the
profiler mechanism for performance reasons so the profiler must be
started to enable tracing.
(JSStartProfiling):
(JSEndProfiling):
API/JSProfilerPrivate.h: Added. Ditto.
JavaScriptCore.exp: Exposing the start/stop methods to clients.