Add test case for replacing turbofan code for debugging.

test/mjsunit/debug-step-turbofan.js

Index: test/mjsunit/debug-step-turbofan.js
diff --git a/test/mjsunit/debug-step-turbofan.js b/test/mjsunit/debug-step-turbofan.js
new file mode 100644
index 0000000000000000000000000000000000000000..c8c346b2c7de1e4470ff961c4be2447045a050d2
--- /dev/null
+++ b/test/mjsunit/debug-step-turbofan.js
@@ -0,0 +1,57 @@
+// Copyright 2014 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: --turbo-filter=g --allow-natives-syntax
+
+// Test that Debug::PrepareForBreakPoints can deal with turbofan code (g)
+// on the stack.  Without deoptimization support, we will not be able to
+// replace optimized code for g by unoptimized code with debug break slots.
+// This would cause stepping to fail (V8 issue 3660).
+
+function f(x) {
+  g(x);
+  var a = 0;              // Break 6
+  return a;               // Break 7
+}                         // Break 8
+
+function g(x) {
+  if (x) h();
+  var a = 0;              // Break 2
+  var b = 1;              // Break 3
+  return a + b;           // Break 4
+}                         // Break 5
+
+function h() {
+  debugger;               // Break 0
+}                         // Break 1
+
+Debug = debug.Debug;
+var exception = null;
+var break_count = 0;
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    exec_state.prepareStep(Debug.StepAction.StepNext, 1);
+    print(exec_state.frame(0).sourceLineText());
+    var match = exec_state.frame(0).sourceLineText().match(/Break (\d)/);
+    assertNotNull(match);
+    assertEquals(break_count++, parseInt(match[1]));
+  } catch (e) {
+    print(e + e.stack);
+    exception = e;
+  }
+}
+
+f(0);
+f(0);
+%OptimizeFunctionOnNextCall(g);
+
+Debug.setListener(listener);
+
+f(1);
+
+Debug.setListener(null);  // Break 9
+assertNull(exception);
+assertEquals(10, break_count);