Fix incorrect coercion of other failures to Failure::Exception in ReThrow.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 9fac06a9f2fb650671e2776e93e95e3036b4b2ab..22a659ae510c081e22f8b33edbd14b703028a950 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -896,13 +896,15 @@ Failure* Isolate::Throw(Object* exception, MessageLocation* location) {
 
 Failure* Isolate::ReThrow(MaybeObject* exception, MessageLocation* location) {
   bool can_be_caught_externally = false;
-  ShouldReportException(&can_be_caught_externally,
-                        is_catchable_by_javascript(exception));
+  bool catchable_by_javascript = is_catchable_by_javascript(exception);
+  ShouldReportException(&can_be_caught_externally, catchable_by_javascript);
+
   thread_local_top()->catcher_ = can_be_caught_externally ?
       try_catch_handler() : NULL;
 
   // Set the exception being re-thrown.
   set_pending_exception(exception);
+  if (exception->IsFailure()) return exception->ToFailureUnchecked();
   return Failure::Exception();
 }