Initial support for native accessibility in ARC

components/exo/surface_observer.h

Index: components/exo/surface_observer.h
diff --git a/components/exo/surface_observer.h b/components/exo/surface_observer.h
index dd27072676e69364d5727a7e2175f4bb53c63fb2..9855ac439e22ab743a7ab768418c321271b17262 100644
--- a/components/exo/surface_observer.h
+++ b/components/exo/surface_observer.h
@@ -5,6 +5,8 @@
 #ifndef COMPONENTS_EXO_SURFACE_OBSERVER_H_
 #define COMPONENTS_EXO_SURFACE_OBSERVER_H_
 
+#include <stdint.h>
+
 namespace exo {
 class Surface;
 
@@ -15,6 +17,9 @@ class SurfaceObserver {
   // chance to remove themselves.
   virtual void OnSurfaceDestroying(Surface* surface) = 0;
 
+  // Called when a surface has an accessibility tree attached or detached.
+  virtual void OnSurfaceAXTreeChanged(int32_t id) {}
+
  protected:
   virtual ~SurfaceObserver() {}
 };