Reduce usage of MessageLoopProxy in base/

chromeos/login/auth/online_attempt_host.h

Index: chromeos/login/auth/online_attempt_host.h
diff --git a/chromeos/login/auth/online_attempt_host.h b/chromeos/login/auth/online_attempt_host.h
index da392450424da68a578fe883776063b4e9c5ec5d..48f3426911b92af9032141c88ee037e88eb85a63 100644
--- a/chromeos/login/auth/online_attempt_host.h
+++ b/chromeos/login/auth/online_attempt_host.h
@@ -14,15 +14,18 @@
 #include "chromeos/login/auth/auth_attempt_state_resolver.h"
 #include "chromeos/login/auth/user_context.h"
 
+namespace base {
+class MessageLoopProxy;
+}  // namespace base
+
 namespace net {
 class URLRequestContextGetter;
-}
+}  // namespace net
 
 namespace chromeos {
 
 class AuthAttemptState;
 class OnlineAttempt;
-class UserContext;
 
 // Helper class which hosts OnlineAttempt for online credentials checking.
 class CHROMEOS_EXPORT OnlineAttemptHost : public AuthAttemptStateResolver {