x11: Remove MessagePumpObserver.

base/message_loop/message_pump_observer.h

Index: base/message_loop/message_pump_observer.h
diff --git a/base/message_loop/message_pump_observer.h b/base/message_loop/message_pump_observer.h
index 1e8a7f53166e4971a0fb37e6ecae904c3a81ad04..d6e7abf786adab9d685e0d616cebd8e32a665358 100644
--- a/base/message_loop/message_pump_observer.h
+++ b/base/message_loop/message_pump_observer.h
@@ -8,16 +8,16 @@
 #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.