Fix --trace-isolates VM crash.

runtime/vm/message_handler.cc

 // Copyright (c) 2011, 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/message_handler.h"
 
 #include "vm/dart.h"
 #include "vm/lockers.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
@@ skipping 364 matching lines @@
         if (ShouldPauseOnExit(status)) {
           // Still paused.
           ASSERT(oob_queue_->IsEmpty());
           task_ = NULL;  // No task in queue.
           return;
         } else {
           PausedOnExitLocked(&ml, false);
         }
       }
       if (FLAG_trace_isolates) {
-        if (status != kOK && isolate() != NULL) {
+        if (status != kOK && thread() != NULL) {
           const Error& error = Error::Handle(thread()->sticky_error());
           OS::Print("[-] Stopping message handler (%s):\n"
                     "\thandler:    %s\n"
                     "\terror:    %s\n",
                     MessageStatusString(status), name(), error.ToCString());
         } else {
           OS::Print("[-] Stopping message handler (%s):\n"
                     "\thandler:    %s\n",
                     MessageStatusString(status), name());
         }
@@ skipping 130 matching lines @@
   handler_->oob_message_handling_allowed_ = false;
 }
 
 
 MessageHandler::AcquiredQueues::~AcquiredQueues() {
   ASSERT(handler_ != NULL);
   handler_->oob_message_handling_allowed_ = true;
 }
 
 }  // namespace dart