[debugger] fix blacklisted tests.

test/mjsunit/es6/default-parameters-debug.js

 // Copyright 2015 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
 
 // Get the Debug object exposed from the debug context global object.
 Debug = debug.Debug
 
 listenerComplete = false;
 breakPointCount = 0;
+exception = null;
 
 function listener(event, exec_state, event_data, data) {
-  if (event == Debug.DebugEvent.Break) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
     breakPointCount++;
     if (breakPointCount == 1) {
       // Break point in initializer for parameter `a`, invoked by
       // initializer for parameter `b`
-      assertEquals('default', exec_state.frame(1).evaluate('mode').value());
-
-      // initializer for `b` can't refer to `b`
-      assertThrows(function() {
-        exec_state.frame(1).evaluate('b').value();
-      }, ReferenceError);
-
-      assertThrows(function() {
-        exec_state.frame(1).evaluate('c');
-      }, ReferenceError);
+      assertEquals('default', exec_state.frame(0).evaluate('mode').value());
+      assertTrue(exec_state.frame(1).evaluate('b').isUndefined());
+      assertTrue(exec_state.frame(1).evaluate('c').isUndefined());
     } else if (breakPointCount == 2) {
       // Break point in IIFE initializer for parameter `c`
       assertEquals('modeFn', exec_state.frame(1).evaluate('a.name').value());
       assertEquals('default', exec_state.frame(1).evaluate('b').value());
-      assertThrows(function() {
-        exec_state.frame(1).evaluate('c');
-      }, ReferenceError);
+      assertTrue(exec_state.frame(1).evaluate('c').isUndefined());
     } else if (breakPointCount == 3) {
       // Break point in function body --- `c` parameter is shadowed
       assertEquals('modeFn', exec_state.frame(0).evaluate('a.name').value());
       assertEquals('default', exec_state.frame(0).evaluate('b').value());
       assertEquals('local', exec_state.frame(0).evaluate('d').value());
     }
+  } catch (e) {
+    exception = e;
   }
 };
 
 // Add the debug event listener.
 Debug.setListener(listener);
 
 function f(a = function modeFn(mode) { debugger; return mode; },
            b = a("default"),
            c = (function() { debugger; })()) {
   var d = 'local';
   debugger;
 };
 
 f();
 
 // Make sure that the debug event listener vas invoked.
 assertEquals(3, breakPointCount);
+assertNull(exception);