[debugger] add test case for stepping into default parameter.

test/mjsunit/harmony/debug-stepin-default-parameters.js

Index: test/mjsunit/harmony/debug-stepin-default-parameters.js
diff --git a/test/mjsunit/harmony/debug-stepin-default-parameters.js b/test/mjsunit/harmony/debug-stepin-default-parameters.js
new file mode 100644
index 0000000000000000000000000000000000000000..1b9c512656d1689cfcc4e31ca2db8960fc32e7d6
--- /dev/null
+++ b/test/mjsunit/harmony/debug-stepin-default-parameters.js
@@ -0,0 +1,46 @@
+// 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 --harmony-default-parameters
+
+Debug = debug.Debug
+
+var exception = null;
+var log = [];
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    print(event_data.sourceLineText());
+    var entry = "";
+    for (var i = 0; i < exec_state.frameCount(); i++) {
+      entry += exec_state.frame(i).sourceLineText().substr(-1);
+      entry += exec_state.frame(i).sourceColumn();
+    }
+    log.push(entry);
+    exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+  } catch (e) {
+    exception = e;
+  }
+};
+
+function default_arg(x) {
+  return "default";                 // d
+}                                   // e
+
+function f(arg0 = default_arg()) {  // f
+  return arg0;                      // g
+}                                   // h
+
+
+Debug.setListener(listener);
+debugger;                           // a
+var result = f();                   // b
+Debug.setListener(null);            // c
+
+assertNull(exception);
+assertEquals("default", result);
+
+assertEquals(["a0","b0","f18b13","d2f18b13","e0f18b13","g2b13","h0b13","c0"],
+             log);