Fix TryCatch.ReThrow() to not clobber Message.

src/isolate.h

Index: src/isolate.h
===================================================================
--- src/isolate.h	(revision 14909)
+++ src/isolate.h	(working copy)
@@ -245,6 +245,7 @@
   ThreadId thread_id_;
   MaybeObject* pending_exception_;
   bool has_pending_message_;
+  bool restoring_message_;
   Object* pending_message_obj_;
   Script* pending_message_script_;
   int pending_message_start_pos_;
@@ -582,6 +583,7 @@
   }
   void clear_pending_message() {
     thread_local_top_.has_pending_message_ = false;
+    thread_local_top_.restoring_message_ = false;
     thread_local_top_.pending_message_obj_ = heap_.the_hole_value();
     thread_local_top_.pending_message_script_ = NULL;
   }
@@ -761,6 +763,9 @@
   // originally.
   Failure* ReThrow(MaybeObject* exception);
   void ScheduleThrow(Object* exception);
+  void RestoreMessage(Object* message, Script* script, int start, int end);
+  // Re-set message, script, position saved in TryCatch to the TLS
+  // so that ReThrow() does not overwrite them with a new message.
   void ReportPendingMessages();
   // Return pending location if any or unfilled structure.
   MessageLocation GetMessageLocation();