exo: Use WMHelper to access ash accessibility related features.

components/exo/wm_helper.cc

Index: components/exo/wm_helper.cc
diff --git a/components/exo/wm_helper.cc b/components/exo/wm_helper.cc
index 6e4b495ba5c8ae3a802ed9575237223eae37bd78..517a4ae414518b419f024c780dee897db8cef52a 100644
--- a/components/exo/wm_helper.cc
+++ b/components/exo/wm_helper.cc
@@ -62,6 +62,14 @@ void WMHelper::RemoveMaximizeModeObserver(MaximizeModeObserver* observer) {
   maximize_mode_observers_.RemoveObserver(observer);
 }
 
+void WMHelper::AddAccessibilityObserver(AccessibilityObserver* observer) {
+  accessibility_observers_.AddObserver(observer);
+}
+
+void WMHelper::RemoveAccessibilityObserver(AccessibilityObserver* observer) {
+  accessibility_observers_.RemoveObserver(observer);
+}
+
 void WMHelper::NotifyWindowActivated(aura::Window* gained_active,
                                      aura::Window* lost_active) {
   FOR_EACH_OBSERVER(ActivationObserver, activation_observers_,
@@ -94,4 +102,9 @@ void WMHelper::NotifyMaximizeModeEnded() {
                     OnMaximizeModeEnded());
 }
 
+void WMHelper::NotifyAccessibilityModeChanged() {
+  FOR_EACH_OBSERVER(AccessibilityObserver, accessibility_observers_,
+                    OnAccessibilityModeChanged());
+}
+
 }  // namespace exo