Extract the shell runner into devtools.

examples/dart/camera_roll/camera_roll.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// To run: mojo/tools/mojo_shell.py --sky \
+// To run: mojo/devtools/common/mojo_shell --sky \
 //             examples/dart/camera_roll/camera_roll.dart --android
 // This example makes use of mojo:camera_roll which is available only when
 // running on Android.
 
 import 'dart:async';
 import 'dart:sky';
 
 import 'package:mojom/mojo/camera_roll.mojom.dart';
 import 'package:sky/mojo/embedder.dart';
 
@@ skipping 39 matching lines @@
   }
 
   return false;
 }
 
 void main() {
   embedder.connectToService("mojo:camera_roll", cameraRoll);
   view.setEventCallback(handleEvent);
   drawNextPhoto();
 }