exo: Use WMHelper to access ash accessibility related features.

components/exo/wm_helper_mus.cc

Index: components/exo/wm_helper_mus.cc
diff --git a/components/exo/wm_helper_mus.cc b/components/exo/wm_helper_mus.cc
index 3f36dbd83ec68f54f9ce12c9990bc3d8e7b76f97..9a67809eae22de12493c3664151aac2917f93565 100644
--- a/components/exo/wm_helper_mus.cc
+++ b/components/exo/wm_helper_mus.cc
@@ -100,6 +100,15 @@ bool WMHelperMus::IsMaximizeModeWindowManagerEnabled() const {
   return false;
 }
 
+bool WMHelperMus::IsSpokenFeedbackEnabled() const {
+  NOTIMPLEMENTED();
+  return false;
+}
+
+void WMHelperMus::PlayEarcon(int sound_key) const {
+  NOTIMPLEMENTED();
+}
+
 void WMHelperMus::OnWindowTreeFocusChanged(ui::Window* gained_focus,
                                            ui::Window* lost_focus) {
   aura::Window* gained_active =