Use signals for cpu profiling on Mac OS X

src/cpu-profiler.cc

Index: src/cpu-profiler.cc
diff --git a/src/cpu-profiler.cc b/src/cpu-profiler.cc
index 47b0de35c4d190fc3a5d1d76b5265a892e65dee6..f8698b31005ce1953c9dd2bb2340e7f5354652e1 100644
--- a/src/cpu-profiler.cc
+++ b/src/cpu-profiler.cc
@@ -436,7 +436,6 @@ void CpuProfiler::StartProcessorIfNotStarted() {
     processor_ = new ProfilerEventsProcessor(
         generator_, sampler, FLAG_cpu_profiler_sampling_interval);
     is_profiling_ = true;
-    processor_->StartSynchronously();
     // Enumerate stuff we already have in the heap.
     ASSERT(isolate_->heap()->HasBeenSetUp());
     if (!FLAG_prof_browser_mode) {
@@ -454,6 +453,7 @@ void CpuProfiler::StartProcessorIfNotStarted() {
       sampler->Start();
       need_to_stop_sampler_ = true;
     }
+    processor_->StartSynchronously();
   }
 }