Fix call stack sampling for the case when native callback invokes JS function

src/frames-inl.h

Index: src/frames-inl.h
diff --git a/src/frames-inl.h b/src/frames-inl.h
index d097ed1dbb5e7a531bc9f1105168b95769b92ddd..2b15bfffab7a984a631e4e20fe3eec0dc06a0b0d 100644
--- a/src/frames-inl.h
+++ b/src/frames-inl.h
@@ -334,10 +334,10 @@ inline JavaScriptFrame* JavaScriptFrameIterator::frame() const {
 }
 
 
-inline JavaScriptFrame* SafeStackFrameIterator::frame() const {
+inline StackFrame* SafeStackFrameIterator::frame() const {
   ASSERT(!done());
-  ASSERT(frame_->is_java_script());
-  return static_cast<JavaScriptFrame*>(frame_);
+  ASSERT(frame_->is_java_script() || frame_->is_exit());
+  return frame_;
 }