Debugger: make debug code on-stack replacement more robust.

test/mjsunit/regress/regress-crbug-507070.js

Index: test/mjsunit/regress/regress-crbug-507070.js
diff --git a/test/mjsunit/regress/regress-crbug-507070.js b/test/mjsunit/regress/regress-crbug-507070.js
new file mode 100644
index 0000000000000000000000000000000000000000..e368fa55177250d824813dd8bc9059ff8623b89f
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-507070.js
@@ -0,0 +1,20 @@
+// 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: --allow-natives-syntax --cache=code
+
+try { } catch(e) { }
+try { try { } catch (e) { } } catch(e) { }
+try {
+  var Debug = %GetDebugContext().Debug;
+  Debug.setListener(function(){});
+} catch(e) { }
+(function() {
+  Debug.setBreakPoint(function(){}, 0, 0);
+})();
+
+var a = 1;
+a += a;
+Debug.setListener(null);
+assertEquals(2, a);