[debugger] flood function for stepping on throw.

test/mjsunit/regress/regress-crbug-568477-4.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 --allow-natives-syntax
 
 var Debug = debug.Debug;
-var expected = ["debugger;", "", "debugger;"];
+var expected =
+    ["debugger;", "var x = y;", "var b = 2;", "Debug.setListener(null);"];
+var log = [];
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
-    assertEquals(expected.shift(), exec_state.frame(0).sourceLineText());
+    log.push(exec_state.frame(0).sourceLineText().trimLeft());
     exec_state.prepareStep(Debug.StepAction.StepNext, 1);
   } catch (e) {
     %AbortJS(e + "\n" + e.stack);
   }
 }
 
 Debug.setListener(listener);
-debugger;
+
+function f() {
+  var a = 1;
+  debugger;
+  var x = y;
+  print(x);
+}
+
+try {
+  %Call(f, {});
+} catch (e) {
+  var b = 2;
+}
+
+Debug.setListener(null);
+
+assertEquals(expected, log);