Make Android Clipboard Keep Track of Last Modified Time

ui/base/clipboard/clipboard.h

Index: ui/base/clipboard/clipboard.h
diff --git a/ui/base/clipboard/clipboard.h b/ui/base/clipboard/clipboard.h
index 8ccb873cfd4ef63c442e1490a6eb9b2125c2bc3e..1c8dc9a16505da9b33fde795b3c8b11af350390b 100644
--- a/ui/base/clipboard/clipboard.h
+++ b/ui/base/clipboard/clipboard.h
@@ -21,6 +21,7 @@
 #include "base/synchronization/lock.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread_checker.h"
+#include "base/time/time.h"
 #include "build/build_config.h"
 #include "ui/base/clipboard/clipboard_types.h"
 #include "ui/base/ui_base_export.h"
@@ -204,6 +205,10 @@ class UI_BASE_EXPORT Clipboard : NON_EXPORTED_BASE(public base::ThreadChecker) {
   virtual void ReadData(const FormatType& format,
                         std::string* result) const = 0;
 
+  // Returns an estimate of the age the clipboard was last updated.
+  // If the last update time is unknown, returns TimeDelta::Max().
+  virtual base::TimeDelta GetClipboardAge() const;
+
   // Gets the FormatType corresponding to an arbitrary format string,
   // registering it with the system if needed. Due to Windows/Linux
   // limitiations, |format_string| must never be controlled by the user.