exo: Fix multi-display hardware cursor

ash/wm/ash_native_cursor_manager.cc

Index: ash/wm/ash_native_cursor_manager.cc
diff --git a/ash/wm/ash_native_cursor_manager.cc b/ash/wm/ash_native_cursor_manager.cc
index 45a3ef82f59b4d8ffeabbd7e72ab466b331897da..dfaa74d882d782cf5601bf6b262646f9ec9cb1a8 100644
--- a/ash/wm/ash_native_cursor_manager.cc
+++ b/ash/wm/ash_native_cursor_manager.cc
@@ -57,6 +57,14 @@ AshNativeCursorManager::AshNativeCursorManager()
 
 AshNativeCursorManager::~AshNativeCursorManager() {}
 
+void AshNativeCursorManager::AddObserver(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void AshNativeCursorManager::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+
 void AshNativeCursorManager::SetNativeCursorEnabled(bool enabled) {
   native_cursor_enabled_ = enabled;
 
@@ -68,6 +76,11 @@ void AshNativeCursorManager::SetDisplay(
     const display::Display& display,
     ::wm::NativeCursorManagerDelegate* delegate) {
   DCHECK(display.is_valid());
+  cursor_display_ = display;
+
+  for (Observer& observer : observers_)
+    observer.OnCursorDisplayChanged(display);
+
   // Use the platform's device scale factor instead of the display's, which
   // might have been adjusted for the UI scale.
   const float original_scale = Shell::Get()