[debugger] correctly find source position of implicit return statement.

test/mjsunit/debug-step-end-of-script.js

Index: test/mjsunit/debug-step-end-of-script.js
diff --git a/test/mjsunit/regress/regress-4309-2.js b/test/mjsunit/debug-step-end-of-script.js
similarity index 59%
copy from test/mjsunit/regress/regress-4309-2.js
copy to test/mjsunit/debug-step-end-of-script.js
index 984b0071c135fd5037d252128d290d7bcc8669cc..5152353cfa9f853b621f3bb51cfb5f5f9726f7b3 100644
--- a/test/mjsunit/regress/regress-4309-2.js
+++ b/test/mjsunit/debug-step-end-of-script.js
@@ -5,30 +5,17 @@
 // Flags: --expose-debug-as debug --allow-natives-syntax
 
 var Debug = debug.Debug;
-
-var exception = null;
+var expected = ["debugger;", "", "debugger;"];
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
-    var scope = exec_state.frame().scope(0);
-    assertEquals(5, scope.scopeObject().property("i").value().value());
+    assertEquals(expected.shift(), exec_state.frame(0).sourceLineText());
+    exec_state.prepareStep(Debug.StepAction.StepNext, 1);
   } catch (e) {
-    exception = e;
+    %AbortJS(e + "\n" + e.stack);
   }
 }
 
-function f() {
-  eval('var i = 5');
-  debugger;
-}
-
-f();
-f();
-
-%OptimizeFunctionOnNextCall(f);
 Debug.setListener(listener);
-
-f();
-
-assertNull(exception);
+debugger;