[debugger] fix blacklisted tests.

test/mjsunit/regress/regress-4703.js

 // Copyright 2016 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
 
+var exception = null;
+
 function listener(event, exec_state, event_data, data) {
-  if (event != Debug.DebugEvent.Break) return;
+  if (event != debug.Debug.DebugEvent.Break) return;
   try {
     var all_scopes = exec_state.frame().allScopes();
     assertEquals([ debug.ScopeType.Block,
                    debug.ScopeType.Local,
                    debug.ScopeType.Script,
                    debug.ScopeType.Global ],
                  all_scopes.map(scope => scope.scopeType()));
   } catch (e) {
     exception = e;
+    print(e);
   }
 }
 
 debug.Debug.setListener(listener);
 
 (function(arg, ...rest) {
   var one = 1;
   function inner() {
     one;
     arg;
   }
   debugger;
 })();
+
+debug.Debug.setListener(null);
+assertNull(exception);