[debugger] Hide scopes that originate from desugaring.

test/mjsunit/es6/regress/regress-468661.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
 
 Debug = debug.Debug
 var exception = null;
 var break_count = 0;
 
 var expected_values =
-  [ReferenceError, undefined, 0, 0, 0, 0, 1, ReferenceError, ReferenceError];
+  [ReferenceError, ReferenceError, 0, 0, 0, 0, 1,
+   ReferenceError, ReferenceError];
 
 function listener(event, exec_state, event_data, data) {
   try {
     if (event == Debug.DebugEvent.Break) {
       assertTrue(exec_state.frameCount() != 0, "FAIL: Empty stack trace");
       // Count number of expected breakpoints in this source file.
       if (!break_count) {
         var source_text = exec_state.frame(0).func().script().source();
         expected_breaks = source_text.match(/\/\/\s*Break\s+\d+\./g).length;
         print("Expected breaks: " + expected_breaks);
       }
       var frameMirror = exec_state.frame(0);
 
       var v = null;;
       try {
         v = frameMirror.evaluate('i').value();
       } catch(e) {
         v = e;
       }
       frameMirror.allScopes();
       var source = frameMirror.sourceLineText();
       print("paused at: " + source);
       assertTrue(source.indexOf("// Break " + break_count + ".") > 0,
                  "Unexpected pause at: " + source + "\n" +
                  "Expected: // Break " + break_count + ".");
       if (expected_values[break_count] === ReferenceError) {
         assertTrue(v instanceof ReferenceError);
       } else {
         assertSame(expected_values[break_count], v);
-
       }
       ++break_count;
 
       if (break_count !== expected_breaks) {
         exec_state.prepareStep(Debug.StepAction.StepIn);
         print("Next step prepared");
       }
     }
   } catch(e) {
     exception = e;
@@ skipping 14 matching lines @@
        i++) {   // Break 5.
     let key = i; // Break 3.
     sum += key;   // Break 4.
   }
 }()); // Break 7.
 
 assertNull(exception); // Break 8.
 assertEquals(expected_breaks, break_count);
 
 Debug.setListener(null);