mash: Move accessibility_types.h from ui namespace to ash namespace

ash/keyboard/keyboard_ui.cc

Index: ash/keyboard/keyboard_ui.cc
diff --git a/ash/keyboard/keyboard_ui.cc b/ash/keyboard/keyboard_ui.cc
index 7022b9cfa19a0e6b9d851f0b1e0e2897197f48b5..1ab3f104d0e0b76168e444f36bda442592e950a0 100644
--- a/ash/keyboard/keyboard_ui.cc
+++ b/ash/keyboard/keyboard_ui.cc
@@ -42,7 +42,7 @@ class KeyboardUIImpl : public KeyboardUI, public AccessibilityObserver {
 
   // AccessibilityObserver:
   void OnAccessibilityModeChanged(
-      ui::AccessibilityNotificationVisibility notify) override {
+      AccessibilityNotificationVisibility notify) override {
     FOR_EACH_OBSERVER(KeyboardUIObserver, *observers(),
                       OnKeyboardEnabledStateChanged(IsEnabled()));
   }