Move stack trace extraction code out of TickSample::Init

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 1595 matching lines @@
    * Returns whether or not the associated function is called as a
    * constructor via "new".
    */
   bool IsConstructor() const;
 };
 
 
 // A StateTag represents a possible state of the VM.
 enum StateTag { JS, GC, COMPILER, OTHER, EXTERNAL, IDLE };
 
-
 // A RegisterState represents the current state of registers used
 // by the sampling profiler API.
 struct RegisterState {
-  RegisterState() : pc(NULL), sp(NULL), fp(NULL) {}
+  RegisterState() : pc(nullptr), sp(nullptr), fp(nullptr) {}
   void* pc;  // Instruction pointer.
   void* sp;  // Stack pointer.
   void* fp;  // Frame pointer.
 };
 
-
 // The output structure filled up by GetStackSample API function.
 struct SampleInfo {
-  size_t frames_count;
-  StateTag vm_state;
+  size_t frames_count;            // Number of frames collected.
+  StateTag vm_state;              // Current VM state.
+  void* external_callback_entry;  // External callback address if VM is
+                                  // executing an external callback.
 };
 
 /**
  * A JSON Parser and Stringifier.
  */
 class V8_EXPORT JSON {
  public:
   /**
    * Tries to parse the string |json_string| and returns it as value if
    * successful.
@@ skipping 7172 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // INCLUDE_V8_H_