Do not eagerly convert exception to string when creating a message object

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index b5e81c55cb239042c63d7147b2b3c56ba4ba7f9e..b63e99dbd5247ca2ba048641b3162ee5811440ba 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -629,7 +629,7 @@ bool Debug::CompileDebuggerScript(Isolate* isolate, int index) {
     DCHECK(!isolate->has_pending_exception());
     MessageLocation computed_location;
     isolate->ComputeLocation(&computed_location);
-    Handle<Object> message = MessageHandler::MakeMessageObject(
+    Handle<JSMessageObject> message = MessageHandler::MakeMessageObject(
         isolate, MessageTemplate::kDebuggerLoading, &computed_location,
         isolate->factory()->undefined_value(), Handle<JSArray>());
     DCHECK(!isolate->has_pending_exception());