x11: Remove MessagePumpObserver.

base/message_loop/message_pump_observer.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_MESSAGE_LOOP_MESSAGE_PUMP_OBSERVER_H
 #define BASE_MESSAGE_LOOP_MESSAGE_PUMP_OBSERVER_H
 
 #include "base/base_export.h"
 #include "base/event_types.h"
 
+#if !defined(OS_WIN)
+#error Should not be here.
+#endif
+
 namespace base {
 
 // A MessagePumpObserver is an object that receives global
-// notifications from the UI MessageLoop with MessagePumpWin or
-// MessagePumpX11.
+// notifications from the UI MessageLoop with MessagePumpWin.
 //
 // NOTE: An Observer implementation should be extremely fast!
-//
-// For use with MessagePumpX11, please see message_pump_glib.h for more
-// info about how this is invoked in this environment.
 class BASE_EXPORT MessagePumpObserver {
  public:
   // This method is called before processing a NativeEvent.
   virtual void WillProcessEvent(const NativeEvent& event) = 0;
 
   // This method is called after processing a message.
   virtual void DidProcessEvent(const NativeEvent& event) = 0;
 
  protected:
   virtual ~MessagePumpObserver() {}
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_MESSAGE_PUMP_OBSERVER_H