Make shake-to-reload actually work

We need to create a new service provider when we navigate to a new page
otherwise the new page is sad that the old page took its service provider.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/962383003

examples/touch-demo.sky

@@ -10,7 +10,7 @@ dot {
     border-radius: 50px;
 }
 </style>
-<log>Ready</log>
+<log>Ready!</log>
 <script>
 import "dart:sky";