Improve rendering of callsite with non-function target.

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

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --expose-debug-as debug --allow-natives-syntax --promise-extra
 
 // Test debug events when an exception is thrown inside a Promise, which is
 // caught by a custom promise, which has no reject handler.
 // We expect two Exception debug events:
 //  1) when the exception is thrown in the promise q.
@@ skipping 30 matching lines @@
     if (event == Debug.DebugEvent.Exception) {
       expected_events--;
       assertTrue(expected_events >= 0);
       if (expected_events == 1) {
         assertTrue(
             exec_state.frame(0).sourceLineText().indexOf('// event') > 0);
         assertEquals("caught", event_data.exception().message);
       } 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();
       }
       assertSame(q, event_data.promise());
     }
   } catch (e) {
     %AbortJS(e + "\n" + e.stack);
   }
 }
@@ skipping 14 matching lines @@
       }
     } catch (e) {
       %AbortJS(e + "\n" + e.stack);
     }
   }
 
   %EnqueueMicrotask(checkResult);
 }
 
 testDone(0);