Don't take a stack trace if we are in the middle of a deoptimization

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 19d410d90c995aed3f4955727772bbc0af585f9f..8d2508fbd9461f131fad072bc8bd4f1390a5f9a8 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -372,6 +372,7 @@ class Isolate : public BaseIsolate {
     return object_id_ring_;
   }
 
+  bool IsDeoptimizing() const { return deopt_context_ != NULL; }
   DeoptContext* deopt_context() const { return deopt_context_; }
   void set_deopt_context(DeoptContext* value) {
     ASSERT(value == NULL || deopt_context_ == NULL);