Change the way sampler / profiler handle external callbacks.

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 78b35e253401912d538862144323d00996ea161f..f836583d9ba9b3daf2a084b17fd65b5ca0bfa22a 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -813,7 +813,15 @@ void ProfileGenerator::RecordTickSample(const TickSample& sample) {
   if (sample.pc != NULL) {
     *entry++ = code_map_.FindEntry(sample.pc);
 
-    if (sample.tos != NULL) {
+    if (sample.has_external_callback) {
+      // Don't use PC when in external callback code, as it can point
+      // inside callback's code, and we will erroneously report
+      // that a callback calls itself.
+      *(entries.start()) = NULL;
+      *entry++ = code_map_.FindEntry(sample.external_callback);
+    } else if (sample.tos != NULL) {
+      // Find out, if top of stack was pointing inside a JS function
+      // meaning that we have encountered a frameless invocation.
       *entry = code_map_.FindEntry(sample.tos);
       if (*entry != NULL && !(*entry)->is_js_function()) {
         *entry = NULL;