exo: Set source for cursor capture requests.

components/exo/pointer.h

Index: components/exo/pointer.h
diff --git a/components/exo/pointer.h b/components/exo/pointer.h
index 24feb2d3db58c49fbf4e29b3446e97ac8cb41c92..67a12efedb18f4ae457f3afc74bcf01d3dc7bf49 100644
--- a/components/exo/pointer.h
+++ b/components/exo/pointer.h
@@ -9,6 +9,7 @@
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/unguessable_token.h"
 #include "components/exo/surface_delegate.h"
 #include "components/exo/surface_observer.h"
 #include "components/exo/wm_helper.h"
@@ -103,6 +104,9 @@ class Pointer : public ui::EventHandler,
   // The current cursor.
   ui::Cursor cursor_;
 
+  // Source used for cursor capture copy output requests.
+  const base::UnguessableToken cursor_capture_source_id_;
+
   // Weak pointer factory used for cursor capture callbacks.
   base::WeakPtrFactory<Pointer> cursor_capture_weak_ptr_factory_;