SelectionOwner: add support for TIMESTAMP target

ui/base/x/selection_owner.h

Index: ui/base/x/selection_owner.h
diff --git a/ui/base/x/selection_owner.h b/ui/base/x/selection_owner.h
index 6ae933aada2f7893a85fb0f5d58867fc131fbc6d..317a70029f0592f4f291acb00c816eae7b3ab2f9 100644
--- a/ui/base/x/selection_owner.h
+++ b/ui/base/x/selection_owner.h
@@ -119,6 +119,9 @@ class UI_BASE_EXPORT SelectionOwner {
   // The X11 selection that this instance communicates on.
   XAtom selection_name_;
 
+  // The time that this instance took ownership of its selection.
+  Time acquired_selection_timestamp_;
+
   // The maximum size of data we can put in XChangeProperty().
   size_t max_request_size_;