Change the way sampler / profiler handle external callbacks.

src/platform.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 563 matching lines @@
 class TickSample {
  public:
   TickSample()
       : state(OTHER),
         pc(NULL),
         sp(NULL),
         fp(NULL),
         tos(NULL),
         frames_count(0) {}
   StateTag state;  // The state of the VM.
-  Address pc;   // Instruction pointer.
-  Address sp;   // Stack pointer.
-  Address fp;   // Frame pointer.
-  Address tos;  // Top stack value (*sp).
+  Address pc;      // Instruction pointer.
+  Address sp;      // Stack pointer.
+  Address fp;      // Frame pointer.
+  union {
+    Address tos;   // Top stack value (*sp).
+    Address external_callback;
+  };
   static const int kMaxFramesCount = 64;
   Address stack[kMaxFramesCount];  // Call stack.
-  int frames_count;  // Number of captured frames.
+  int frames_count : 8;  // Number of captured frames.
+  bool has_external_callback : 1;
 };
 
 #ifdef ENABLE_LOGGING_AND_PROFILING
 class Sampler {
  public:
   // Initialize sampler.
   Sampler(Isolate* isolate, int interval);
   virtual ~Sampler();
 
   int interval() const { return interval_; }
@@ skipping 46 matching lines @@
   int samples_taken_;  // Counts stack samples taken.
   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
 };
 
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal
 
 #endif  // V8_PLATFORM_H_