Fix hidden bug with isolate shutdown debugger events

runtime/vm/service_isolate.cc

 // Copyright (c) 2015, 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.
 
 #include "vm/service_isolate.h"
 
 #include "vm/compiler.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/isolate.h"
@@ skipping 502 matching lines @@
   port_ = port;
 }
 
 
 void ServiceIsolate::SetServiceIsolate(Isolate* isolate) {
   MonitorLocker ml(monitor_);
   isolate_ = isolate;
   if (isolate_ != NULL) {
     isolate_->is_service_isolate_ = true;
     origin_ = isolate_->origin_id();
-  } else {
-    origin_ = ILLEGAL_PORT;
   }
 }
 
 void ServiceIsolate::SetLoadPort(Dart_Port port) {
   MonitorLocker ml(monitor_);
   load_port_ = port;
 }
 
 
 void ServiceIsolate::MaybeInjectVMServiceLibrary(Isolate* I) {
@@ skipping 312 matching lines @@
     return result;
   }
   Dart_Handle source = GetSource(url_string);
   if (Dart_IsError(source)) {
     return source;
   }
   return Dart_LoadSource(library, url, source, 0, 0);
 }
 
 }  // namespace dart