Try to simplify the semantics of the profiling code by making...

src/log.cc

 // Copyright 2009 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 173 matching lines @@
 // Ticker used to provide ticks to the profiler and the sliding state
 // window.
 //
 class Ticker: public Sampler {
  public:
   explicit Ticker(int interval):
       Sampler(interval, FLAG_prof), window_(NULL), profiler_(NULL) {}
 
   ~Ticker() { if (IsActive()) Stop(); }
 
-  void SampleStack(TickSample* sample) {
+  virtual void SampleStack(TickSample* sample) {
+    ASSERT(IsSynchronous());
     StackTracer::Trace(sample);
   }
 
-  void Tick(TickSample* sample) {
+  virtual void Tick(TickSample* sample) {
     if (profiler_) profiler_->Insert(sample);
     if (window_) window_->AddState(sample->state);
   }
 
   void SetWindow(SlidingStateWindow* window) {
     window_ = window;
     if (!IsActive()) Start();
   }
 
   void ClearWindow() {
@@ skipping 1378 matching lines @@
   }
   // Otherwise, if the sliding state window computation has not been
   // started we do it now.
   if (sliding_state_window_ == NULL) {
     sliding_state_window_ = new SlidingStateWindow();
   }
 #endif
 }
 
 } }  // namespace v8::internal