[debug] Don't notify listener of exceptions internal to a desugaring.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 32845124822c61d60be45e9bc4c4acaadc8ae7bb..bc0161943cd118ff7991225f73a3fd4538fecb02 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -748,7 +748,12 @@ class Isolate {
   // Tries to predict whether an exception will be caught. Note that this can
   // only produce an estimate, because it is undecidable whether a finally
   // clause will consume or re-throw an exception.
-  enum CatchType { NOT_CAUGHT, CAUGHT_BY_JAVASCRIPT, CAUGHT_BY_EXTERNAL };
+  enum CatchType {
+    NOT_CAUGHT,
+    CAUGHT_BY_JAVASCRIPT,
+    CAUGHT_BY_EXTERNAL,
+    CAUGHT_BY_DESUGARING
+  };
   CatchType PredictExceptionCatcher();
 
   void ScheduleThrow(Object* exception);