Fix some service protocol isolate lifecycle races

runtime/observatory/lib/src/app/application.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of app;
 
 class Notification {
   Notification.fromEvent(this.event);
   Notification.fromException(this.exception, this.stacktrace);
 
@@ skipping 91 matching lines @@
       case ServiceEvent.kIsolateExit:
       case ServiceEvent.kResume:
         removePauseEvents(event.isolate);
         break;
 
       case ServiceEvent.kPauseStart:
       case ServiceEvent.kPauseExit:
       case ServiceEvent.kPauseBreakpoint:
       case ServiceEvent.kPauseInterrupted:
       case ServiceEvent.kPauseException:
+      case ServiceEvent.kPauseUntilRunnable:

[turnidge, 2016/03/03 17:15:01]

We will never receive this event.  Maybe make it its own case which asserts not
received or move to default case?

[Cutch, 2016/03/03 19:22:00]

Done.

         removePauseEvents(event.isolate);
         notifications.add(new Notification.fromEvent(event));
         break;
 
       case ServiceEvent.kInspect:
         notifications.add(new Notification.fromEvent(event));
         break;
 
       default:
         // Ignore unrecognized events.
@@ skipping 112 matching lines @@
     }
 
     // TODO(turnidge): Report this failure via analytics.
     Logger.root.warning('Caught exception: ${e}\n${st}');
     notifications.add(new Notification.fromException(e, st));
   }
 
   // This map keeps track of which curly-blocks have been expanded by the user.
   Map<String,bool> expansions = {};
 }