Make sure debugger is ready for breakpoins when we process 'debugger' statement.

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;
 
@@ skipping 11 matching lines @@
         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);
       }
@@ skipping 23 matching lines @@
        i++) {
     let key = i; // Break 4.
     sum += key;   // Break 5.
   }
 }()); // Break 8.
 
 assertNull(exception); // Break 9.
 assertEquals(expected_breaks, break_count);
 
 Debug.setListener(null);