[debugger] fix blacklisted tests.

test/mjsunit/regress/regress-2296.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 12 matching lines @@
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Flags: --expose-debug-as debug
 
 Debug = debug.Debug
 
 function listener(event, exec_state, event_data, data) {
-  event_data.script().setSource(1);
+  try {
+    event_data.script().setSource(1);
+  } catch (e) {
+    assertTrue(String(e).indexOf("Source is not a string") > 0);
+  }
 };
 
 Debug.setListener(listener);
 
 eval('0');
 
 Debug.setListener(null);