Use factory to create histograms, and refcounts to track lifetimes...

base/message_loop.h

 // 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.
 
 #ifndef BASE_MESSAGE_LOOP_H_
 #define BASE_MESSAGE_LOOP_H_
 
 #include <queue>
 #include <string>
 
@@ skipping 379 matching lines @@
   ObserverList<DestructionObserver> destruction_observers_;
 
   // A recursion block that prevents accidentally running additonal tasks when
   // insider a (accidentally induced?) nested message pump.
   bool nestable_tasks_allowed_;
 
   bool exception_restoration_;
 
   std::string thread_name_;
   // A profiling histogram showing the counts of various messages and events.
-  scoped_ptr<LinearHistogram> message_histogram_;
+  scoped_refptr<Histogram> message_histogram_;
 
   // A null terminated list which creates an incoming_queue of tasks that are
   // aquired under a mutex for processing on this instance's thread. These tasks
   // have not yet been sorted out into items for our work_queue_ vs items that
   // will be handled by the TimerManager.
   TaskQueue incoming_queue_;
   // Protect access to incoming_queue_.
   Lock incoming_queue_lock_;
 
   RunState* state_;
@@ skipping 103 matching lines @@
 #endif  // defined(OS_POSIX)
 };
 
 // Do not add any member variables to MessageLoopForIO!  This is important b/c
 // MessageLoopForIO is often allocated via MessageLoop(TYPE_IO).  Any extra
 // data that you need should be stored on the MessageLoop's pump_ instance.
 COMPILE_ASSERT(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
                MessageLoopForIO_should_not_have_extra_member_variables);
 
 #endif  // BASE_MESSAGE_LOOP_H_