Revert 212948 "Made MessagePump a non-thread safe class."

trunk/src/base/message_loop/message_pump_default.h

Index: trunk/src/base/message_loop/message_pump_default.h
===================================================================
--- trunk/src/base/message_loop/message_pump_default.h	(revision 212951)
+++ trunk/src/base/message_loop/message_pump_default.h	(working copy)
@@ -14,7 +14,6 @@
 class MessagePumpDefault : public MessagePump {
  public:
   MessagePumpDefault();
-  virtual ~MessagePumpDefault();
 
   // MessagePump methods:
   virtual void Run(Delegate* delegate) OVERRIDE;
@@ -22,6 +21,9 @@
   virtual void ScheduleWork() OVERRIDE;
   virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time) OVERRIDE;
 
+ protected:
+  virtual ~MessagePumpDefault() {}
+
  private:
   // This flag is set to false when Run should return.
   bool keep_running_;