Do not store fp and sp values in TickSample

src/sampler.h

Index: src/sampler.h
diff --git a/src/sampler.h b/src/sampler.h
index 3875a29e663e1bb8c797553515e820f56eb7ff14..63e6cfe15af6457e5405ba0761b845ad3c2dbdff 100644
--- a/src/sampler.h
+++ b/src/sampler.h
@@ -43,22 +43,25 @@ class Isolate;
 // (if used for profiling) the program counter and stack pointer for
 // the thread that created it.
 
+struct RegisterState {
+  RegisterState() : pc(NULL), sp(NULL), fp(NULL) {}
+  Address pc;      // Instruction pointer.
+  Address sp;      // Stack pointer.
+  Address fp;      // Frame pointer.
+};
+
 // TickSample captures the information collected for each sample.
 struct TickSample {
   TickSample()
       : state(OTHER),
         pc(NULL),
-        sp(NULL),
-        fp(NULL),
         external_callback(NULL),
         frames_count(0),
         has_external_callback(false),
         top_frame_type(StackFrame::NONE) {}
-  void Trace(Isolate* isolate);
+  void Init(Isolate* isolate, const RegisterState& state);
   StateTag state;  // The state of the VM.
   Address pc;      // Instruction pointer.
-  Address sp;      // Stack pointer.
-  Address fp;      // Frame pointer.
   union {
     Address tos;   // Top stack value (*sp).
     Address external_callback;
@@ -84,11 +87,7 @@ class Sampler {
   int interval() const { return interval_; }
 
   // Performs stack sampling.
-  void SampleStack(TickSample* sample);
-
-  // This method is called for each sampling period with the current
-  // program counter.
-  virtual void Tick(TickSample* sample) = 0;
+  void SampleStack(const RegisterState& regs);
 
   // Start and stop sampler.
   void Start();
@@ -109,6 +108,11 @@ class Sampler {
   class PlatformData;
   PlatformData* platform_data() const { return data_; }
 
+ protected:
+  // This method is called for each sampling period with the current
+  // program counter.
+  virtual void Tick(TickSample* sample) = 0;
+
  private:
   void SetActive(bool value) { NoBarrier_Store(&active_, value); }