ash: Cleanup class/struct forward declarations

ash/system/chromeos/rotation/tray_rotation_lock.h

Index: ash/system/chromeos/rotation/tray_rotation_lock.h
diff --git a/ash/system/chromeos/rotation/tray_rotation_lock.h b/ash/system/chromeos/rotation/tray_rotation_lock.h
index 8df5324b2390beea308b852632ae3502f1234a60..0576f427f559594edfac90fabbab935897a31ad0 100644
--- a/ash/system/chromeos/rotation/tray_rotation_lock.h
+++ b/ash/system/chromeos/rotation/tray_rotation_lock.h
@@ -12,10 +12,6 @@
 
 namespace ash {
 
-namespace tray {
-class RotationLockDefaultView;
-}  // namespace tray
-
 // TrayRotationLock is a provider of views for the SystemTray. Both a tray view
 // and a default view are provided. Each view indicates the current state of
 // the rotation lock for the display which it appears on. The default view can