exo: Fix multi-display hardware cursor

ash/wm/ash_native_cursor_manager.h

Index: ash/wm/ash_native_cursor_manager.h
diff --git a/ash/wm/ash_native_cursor_manager.h b/ash/wm/ash_native_cursor_manager.h
index fac694dd960fa93e45f9c3272d8ba0fbed57a71b..4e2f20d2ff97338ff24a54def8c4453cb9a1cbcf 100644
--- a/ash/wm/ash_native_cursor_manager.h
+++ b/ash/wm/ash_native_cursor_manager.h
@@ -10,6 +10,7 @@
 #include "ash/ash_export.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/native_widget_types.h"
@@ -32,9 +33,20 @@ class CursorManagerTestApi;
 // changes were acted on.
 class ASH_EXPORT AshNativeCursorManager : public ::wm::NativeCursorManager {
  public:
+  class Observer {
+   public:
+    virtual void OnCursorDisplayChanging(const display::Display& display) = 0;
+
+   protected:
+    virtual ~Observer() {}
+  };
+
   AshNativeCursorManager();
   ~AshNativeCursorManager() override;
 
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
   // Toggle native cursor enabled/disabled.
   // The native cursor is enabled by default. When disabled, we hide the native
   // cursor regardless of visibility state, and let CursorWindowManager draw
@@ -64,6 +76,8 @@ class ASH_EXPORT AshNativeCursorManager : public ::wm::NativeCursorManager {
 
   std::unique_ptr<ui::ImageCursors> image_cursors_;
 
+  base::ObserverList<Observer> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(AshNativeCursorManager);
 };