Refactor isolate interrupts to use OOB messages instead of interrupt bits.

runtime/observatory/lib/src/elements/debugger.dart

 // Copyright (c) 2014, 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.
 
 library debugger_page_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:observatory/app.dart';
@@ skipping 1366 matching lines @@
           console.print('Paused due to exception at '
                         '${script.name}:${line}:${col}');
           // This seems to be missing if we are paused-at-exception after
           // paused-at-isolate-exit. Maybe we shutdown part of the debugger too
           // soon?
           console.printRef(event.exception);
         } else {
           console.print('Paused at ${script.name}:${line}:${col}');
         }
       });
+    } else {
+          console.print("Paused in message loop (type 'continue' or [F7] "
+                        "to resume processing messages)");
     }
   }
 
   Future _reportBreakpointEvent(ServiceEvent event) async {
     var bpt = event.breakpoint;
     var verb = null;
     switch (event.kind) {
       case ServiceEvent.kBreakpointAdded:
         verb = 'added';
         break;
@@ skipping 959 matching lines @@
         }
       });
   }
 
   void focus() {
     $['textBox'].focus();
   }
 
   DebuggerInputElement.created() : super.created();
 }