Revert r14252 as it broke --prof for some cases

src/sampler.cc

 // Copyright 2013 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 618 matching lines @@
   // Avoid collecting traces while doing GC.
   if (state == GC) return;
 
   const Address js_entry_sp =
       Isolate::js_entry_sp(isolate->thread_local_top());
   if (js_entry_sp == 0) {
     // Not executing JS now.
     return;
   }
 
-  external_callback = isolate->external_callback();
+  const Address callback = isolate->external_callback();
+  if (callback != NULL) {
+    external_callback = callback;
+    has_external_callback = true;
+  } else {
+    // Sample potential return address value for frameless invocation of
+    // stubs (we'll figure out later, if this value makes sense).
+    tos = Memory::Address_at(sp);
+    has_external_callback = false;
+  }
 
   SafeStackTraceFrameIterator it(isolate, fp, sp, sp, js_entry_sp);
   int i = 0;
   while (!it.done() && i < TickSample::kMaxFramesCount) {
     stack[i++] = it.frame()->pc();
     it.Advance();
   }
   frames_count = i;
 }
 
@@ skipping 35 matching lines @@
   SamplerThread::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 void Sampler::SampleStack(TickSample* sample) {
   sample->Trace(isolate_);
   if (++samples_taken_ < 0) samples_taken_ = 0;
 }
 
 } }  // namespace v8::internal