Fix reporting of impossible nested calls of DOM functions.

src/log.cc

Index: src/log.cc
diff --git a/src/log.cc b/src/log.cc
index 2cc2b8ffa85fd9892a9ab0c4c7f5522bd251a911..d12aafb6df87e59c877d7ff775c8f05a57d59cf5 100644
--- a/src/log.cc
+++ b/src/log.cc
@@ -164,7 +164,10 @@ void StackTracer::Trace(TickSample* sample) {
 
   int i = 0;
   const Address callback = VMState::external_callback();
-  if (callback != NULL) {
+  // Surprisingly, PC can point _exactly_ to callback start, with good
+  // probability, and this will result in reporting fake nested
+  // callback call.
+  if (callback != NULL && callback != sample->pc) {
     sample->stack[i++] = callback;
   }