Fixes shutdown crashes.

runtime/bin/dbg_message.cc

 // Copyright (c) 2012, 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 "bin/dbg_connection.h"
 #include "bin/dbg_message.h"
 #include "bin/dartutils.h"
 #include "bin/lockers.h"
 #include "bin/thread.h"
 #include "bin/utils.h"
@@ skipping 1391 matching lines @@
 
 void DbgMsgQueueList::IsolateEventHandler(Dart_IsolateId isolate_id,
                                           Dart_IsolateEvent kind) {
   if (kind == kCreated) {
     DebuggerConnectionHandler::WaitForConnection();
     Dart_EnterScope();
     DbgMsgQueue* msg_queue = AddIsolateMsgQueue(isolate_id);
     msg_queue->SendIsolateEvent(isolate_id, kind);
     Dart_ExitScope();
   } else {
-    DebuggerConnectionHandler::WaitForConnection();
     DbgMsgQueue* msg_queue = GetIsolateMsgQueue(isolate_id);
-    ASSERT(msg_queue != NULL);
-    Dart_EnterScope();
-    msg_queue->SendQueuedMsgs();
-    msg_queue->SendIsolateEvent(isolate_id, kind);
-    if (kind == kInterrupted) {
-      msg_queue->MessageLoop();
-    } else {
-      ASSERT(kind == kShutdown);
-      RemoveIsolateMsgQueue(isolate_id);
-    }
-    Dart_ExitScope();
     // If there is no receive message queue, do not wait for a connection, and
     // ignore the message.
+    if (msg_queue != NULL) {

[zra, 2015/10/26 20:51:10]

The vm isolate does not have a debug message queue.

+      DebuggerConnectionHandler::WaitForConnection();
+      Dart_EnterScope();
+      msg_queue->SendQueuedMsgs();
+      msg_queue->SendIsolateEvent(isolate_id, kind);
+      if (kind == kInterrupted) {
+        msg_queue->MessageLoop();
+      } else {
+        ASSERT(kind == kShutdown);
+        RemoveIsolateMsgQueue(isolate_id);
+      }
+      Dart_ExitScope();
+    }
   }
 }
 
 }  // namespace bin
 }  // namespace dart