Fix mojodb to use the new sky_server API also.

sky/HACKING.md

 Hacking on Sky
 ==============
 
 Building
 --------
 
 * Follow the setup & build instructions for [Mojo](https://github.com/domokit/mojo)
 
 The build directory will be `out/Debug` for Linux debug builds, and
 `out/Release` for Linux release builds. For Android builds, prefix
@@ skipping 42 matching lines @@
 * Type the URL you wish to run, for example ``http://127.0.0.1:8000/sky/tests/widgets/dialog.dart``, and press the enter key
 * The harness should print the results of the test.  You can then type another URL.
 
 Writing tests
 -------------
 
 We recommend using the [Dart
 ``test``](https://pub.dartlang.org/packages/test) testing framework.
 See [``sky/tests/raw/color_bounds.dart``](tests/raw/color_bounds.dart)
 for an example.
+
+Debugging Sky
+-------------
+
+This document aims to explain how to debug Sky itself.
+
+=== C++
+
+Launch a debug Sky build on Linux as follows (where `app.dart` is the
+test you are running and trying to debug):
+
+```bash
+mojodb start --gdb out/Debug app.dart

[eseidel, 2015/06/22 21:28:18]

These are soon to be deprecated instructions, care of the dev_tools work from
Paris.  You'd have to ask them what the new flow is however.  It may be
documented on mojo-dev.

+mojodb gdb_attach
+```
+
+=== Dart
+
+Use Observatory.