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

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 545 matching lines @@
   virtual void SampleStack(TickSample* sample) = 0;
 
   // This method is called for each sampling period with the current
   // program counter.
   virtual void Tick(TickSample* sample) = 0;
 
   // Start and stop sampler.
   void Start();
   void Stop();
 
-  // Is the sampler used for profiling.
-  inline bool IsProfiling() { return profiling_; }
+  // Is the sampler used for profiling?
+  bool IsProfiling() const { return profiling_; }
+
+  // Is the sampler running in sync with the JS thread? On platforms
+  // where the sampler is implemented with a thread that wakes up
+  // every now and then, having a synchronous sampler implies
+  // suspending/resuming the JS thread.
+  bool IsSynchronous() const { return synchronous_; }
 
   // Whether the sampler is running (that is, consumes resources).
-  inline bool IsActive() { return active_; }
+  bool IsActive() const { return active_; }
 
   class PlatformData;
 
  private:
   const int interval_;
   const bool profiling_;
+  const bool synchronous_;
   bool active_;
   PlatformData* data_;  // Platform specific data.
   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
 };
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal
 
 #endif  // V8_PLATFORM_H_