Fix NSPasteboard leaks.

ui/base/clipboard/clipboard_util_mac.h

Index: ui/base/clipboard/clipboard_util_mac.h
diff --git a/ui/base/clipboard/clipboard_util_mac.h b/ui/base/clipboard/clipboard_util_mac.h
index 79a2a6910be3d308c0cee49674ebed8a8cc0e37f..2bb6edaf36eb5b875ef239efb8fee16ab7182895 100644
--- a/ui/base/clipboard/clipboard_util_mac.h
+++ b/ui/base/clipboard/clipboard_util_mac.h
@@ -8,10 +8,24 @@
 #import <AppKit/AppKit.h>
 
 #include "base/mac/scoped_nsobject.h"
+#include "base/memory/ref_counted.h"
 #include "ui/base/ui_base_export.h"
 
 namespace ui {
 
+class UI_BASE_EXPORT UniquePasteboard
+    : public base::RefCounted<UniquePasteboard> {
+ public:
+  UniquePasteboard();
+
+  NSPasteboard* get() { return pasteboard_; }
+
+ private:
+  friend class base::RefCounted<UniquePasteboard>;
+  ~UniquePasteboard();
+  base::scoped_nsobject<NSPasteboard> pasteboard_;
+};
+
 class UI_BASE_EXPORT ClipboardUtil {
  public:
   // Returns an NSPasteboardItem that represents the given |url|.