x11: Remove MessagePumpObserver.

Convert the last ramining instances of MessagePumpObservers into
PlatformEventObservers, and remove support for MessagePumpObservers
from non-Windows platforms.

BUG=354062
R=sky@chromium.org
TBR=darin@chromium.org

Review URL: https://codereview.chromium.org/233653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@263158 0039d316-1c4b-4281-b951-d872f2087c98


CrOS-Libchrome-Original-Commit: e10f5fe11f4e034f7e12bd5cf4ab0a9d11bb8639
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index 5f51fb7..6bea30c 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -669,8 +669,7 @@
 }
 #endif
 
-#if !defined(OS_NACL) && (defined(TOOLKIT_GTK) || \
-                          defined(OS_WIN) || defined(USE_X11))
+#if !defined(OS_NACL) && defined(OS_WIN)
 void MessageLoopForUI::AddObserver(Observer* observer) {
   pump_ui()->AddObserver(observer);
 }
@@ -678,7 +677,7 @@
 void MessageLoopForUI::RemoveObserver(Observer* observer) {
   pump_ui()->RemoveObserver(observer);
 }
-#endif  //  !defined(OS_MACOSX) && !defined(OS_NACL) && !defined(OS_ANDROID)
+#endif  // !defined(OS_NACL) && defined(OS_WIN)
 
 #if defined(USE_OZONE) && !defined(OS_NACL)
 bool MessageLoopForUI::WatchFileDescriptor(