Expose Thread::using_external_message_loop() to subclasses.

base/threading/thread.h

 // Copyright (c) 2012 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.
 
 #ifndef BASE_THREADING_THREAD_H_
 #define BASE_THREADING_THREAD_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 226 matching lines @@
 
   // Called just after the message loop ends
   virtual void CleanUp() {}
 
   static void SetThreadWasQuitProperly(bool flag);
   static bool GetThreadWasQuitProperly();
 
   // Bind this Thread to an existing MessageLoop instead of starting a new one.
   void SetMessageLoop(MessageLoop* message_loop);
 
+  bool using_external_message_loop() const {
+    return using_external_message_loop_;
+  }
+
  private:
 #if defined(OS_WIN)
   enum ComStatus {
     NONE,
     STA,
     MTA,
   };
 #endif
 
   // PlatformThread::Delegate methods:
@@ skipping 29 matching lines @@
   // Protects |id_| which must only be read while it's signaled.
   mutable WaitableEvent id_event_;
 
   // The thread's MessageLoop and RunLoop. Valid only while the thread is alive.
   // Set by the created thread.
   MessageLoop* message_loop_ = nullptr;
   RunLoop* run_loop_ = nullptr;
 
   // True only if |message_loop_| was externally provided by |SetMessageLoop()|
   // in which case this Thread has no underlying |thread_| and should merely
-  // drop |message_loop_| on Stop().
+  // drop |message_loop_| on Stop(). In that event, this remains true after
+  // Stop() was invoked so that subclasses can use this state to build their own
+  // cleanup logic as required.
   bool using_external_message_loop_ = false;
 
   // Stores Options::timer_slack_ until the message loop has been bound to
   // a thread.
   TimerSlack message_loop_timer_slack_ = TIMER_SLACK_NONE;
 
   // The name of the thread.  Used for debugging purposes.
   const std::string name_;
 
   // Signaled when the created thread gets ready to use the message loop.
   mutable WaitableEvent start_event_;
 
   // This class is not thread-safe, use this to verify access from the owning
   // sequence of the Thread.
   SequenceChecker owning_sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_H_