Thread::Stop() must be called before any subclass's destructor completes.

chrome/browser/printing/print_job_worker.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/printing/print_job_worker.h"
 
 #include "base/message_loop.h"
 #include "base/values.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/printing/print_job.h"
@@ skipping 50 matching lines @@
 
   printing_context_.reset(PrintingContext::Create(
       g_browser_process->GetApplicationLocale()));
 }
 
 PrintJobWorker::~PrintJobWorker() {
   // The object is normally deleted in the UI thread, but when the user
   // cancels printing or in the case of print preview, the worker is destroyed
   // on the I/O thread.
   DCHECK_EQ(owner_->message_loop(), MessageLoop::current());
+  Stop();
 }
 
 void PrintJobWorker::SetNewOwner(PrintJobWorkerOwner* new_owner) {
   DCHECK(page_number_ == PageNumber::npos());
   owner_ = new_owner;
 }
 
 void PrintJobWorker::GetSettings(bool ask_user_for_settings,
                                  gfx::NativeView parent_view,
                                  int document_page_count,
@@ skipping 278 matching lines @@
     printing::PrintJobWorker* obj) {
   DCHECK(!owner_.get());
   owner_ = obj->owner_;
 }
 
 void RunnableMethodTraits<printing::PrintJobWorker>::ReleaseCallee(
     printing::PrintJobWorker* obj) {
   DCHECK_EQ(owner_, obj->owner_);
   owner_ = NULL;
 }