Add superficial unit test for PrintJob. That's a start....

base/thread.cc

 // Copyright (c) 2006-2008 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 "base/thread.h"
 
 #include "base/lazy_instance.h"
 #include "base/string_util.h"
 #include "base/thread_local.h"
 #include "base/waitable_event.h"
@@ skipping 113 matching lines @@
 
   // We should only be called on the same thread that started us.
   DCHECK_NE(thread_id_, PlatformThread::CurrentId());
 
   // We had better have a message loop at this point!  If we do not, then it
   // most likely means that the thread terminated unexpectedly, probably due
   // to someone calling Quit() on our message loop directly.
   DCHECK(message_loop_);
 
   message_loop_->PostTask(FROM_HERE, new ThreadQuitTask());
-
-  // The thread can't receive messages anymore.
-  message_loop_ = NULL;
 }
 
 void Thread::ThreadMain() {
   // The message loop for this thread.
   MessageLoop message_loop(startup_data_->options.message_loop_type);
 
   // Complete the initialization of our Thread object.
   thread_id_ = PlatformThread::CurrentId();
   PlatformThread::SetName(name_.c_str());
   message_loop.set_thread_name(name_);
@@ skipping 12 matching lines @@
   CleanUp();
 
   // Assert that MessageLoop::Quit was called by ThreadQuitTask.
   DCHECK(GetThreadWasQuitProperly());
 
   // We can't receive messages anymore.
   message_loop_ = NULL;
 }
 
 }  // namespace base