Improve rendering of callsite with non-function target.

test/mjsunit/es6/debug-promises/throw-with-undefined-reject.js

Index: test/mjsunit/es6/debug-promises/throw-with-undefined-reject.js
diff --git a/test/mjsunit/es6/debug-promises/throw-with-undefined-reject.js b/test/mjsunit/es6/debug-promises/throw-with-undefined-reject.js
index 7fa60f86cf05c4fda779d4a9b22b185b76a1217b..69ee01ee41fd64d7ac7d1e765f8b96908630e8f4 100644
--- a/test/mjsunit/es6/debug-promises/throw-with-undefined-reject.js
+++ b/test/mjsunit/es6/debug-promises/throw-with-undefined-reject.js
@@ -48,7 +48,7 @@ function listener(event, exec_state, event_data, data) {
       } else if (expected_events == 0) {
         // All of the frames on the stack are from native Javascript.
         assertEquals(0, exec_state.frameCount());
-        assertEquals("undefined is not a function",
+        assertEquals("(var).reject is not a function",
                      event_data.exception().message);
       } else {
         assertUnreachable();