Get rid of UnsafeCurrent in Sampler

src/profiler/sampler.h

Index: src/profiler/sampler.h
diff --git a/src/profiler/sampler.h b/src/profiler/sampler.h
index dcd1255d7578a8c8da60dcab9cf34ce78c48aca5..99233582c0830ecee2bd272e5cbce8b9ab75aef4 100644
--- a/src/profiler/sampler.h
+++ b/src/profiler/sampler.h
@@ -92,6 +92,10 @@ class Sampler {
   // Whether the sampler is running (that is, consumes resources).
   bool IsActive() const { return base::NoBarrier_Load(&active_); }
 
+  // A sampler can be registered when Start() doesn't get called,
+  // since CpuProfiler won't start the sampler but need to collect samples.

[fmeawad, 2016/04/06 20:07:56]

I would rephrase this as 
// CpuProfiler collects samples without calling Start, to avoid deleting the
sampler while in use by the CpuProfiler we register it.

(or something similar)

[lpy, 2016/04/06 20:19:58]

Done.

+  bool IsRegistered() const { return base::NoBarrier_Load(&registered_); }
+
   void DoSample();
   // If true next sample must be initiated on the profiler event processor
   // thread right after latest sample is processed.
@@ -119,11 +123,14 @@ class Sampler {
  private:
   void SetActive(bool value) { base::NoBarrier_Store(&active_, value); }
 
+  void SetRegistered(bool value) { base::NoBarrier_Store(&registered_, value); }
+
   Isolate* isolate_;
   const int interval_;
   base::Atomic32 profiling_;
   base::Atomic32 has_processing_thread_;
   base::Atomic32 active_;
+  base::Atomic32 registered_;
   PlatformData* data_;  // Platform specific data.
   // Counts stack samples taken in various VM states.
   bool is_counting_samples_;