[debugger] Hide scopes that originate from desugaring.

test/mjsunit/debug-scopes.js

 // Copyright 2011 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 1161 matching lines @@
 BeginTest("Scope positions in for statement");
 var code3 = "function for_statement() {         \n" +
             "  for (let i = 0; i < 1; i++) {    \n" +
             "    debugger;                      \n" +
             "  }                                \n" +
             "}                                  \n" +
             "for_statement();                   \n";
 
 listener_delegate = function(exec_state) {
   CheckScopeChain([debug.ScopeType.Block,
-                   debug.ScopeType.Block,
                    debug.ScopeType.Local,
                    debug.ScopeType.Script,
                    debug.ScopeType.Global], exec_state);
-  CheckScopeChainPositions([{start: 52, end: 111}, {start: 42, end: 111}, {start: 22, end: 145}, {}, {}], exec_state);
+  CheckScopeChainPositions([{start: 52, end: 111}, {start: 22, end: 145}, {}, {}], exec_state);
 }
 eval(code3);
 EndTest();
 
 assertEquals(begin_test_count, break_count,
              'one or more tests did not enter the debugger');
 assertEquals(begin_test_count, end_test_count,
              'one or more tests did not have its result checked');