Make Clipboard::FormatType an opaque handle type.

ui/base/clipboard/scoped_clipboard_writer.h

Index: ui/base/clipboard/scoped_clipboard_writer.h
diff --git a/ui/base/clipboard/scoped_clipboard_writer.h b/ui/base/clipboard/scoped_clipboard_writer.h
index 3e224a2465a7ee2712f5ab5fd5e0699518f6aed9..08aaa3a21b9625fabeb5d4b2b24d71e31bbab200 100644
--- a/ui/base/clipboard/scoped_clipboard_writer.h
+++ b/ui/base/clipboard/scoped_clipboard_writer.h
@@ -60,7 +60,8 @@ class UI_EXPORT ScopedClipboardWriter {
   void WriteBitmapFromPixels(const void* pixels, const gfx::Size& size);
 
   // Adds arbitrary data to clipboard.
-  void WritePickledData(const Pickle& pickle, Clipboard::FormatType format);
+  void WritePickledData(const Pickle& pickle,
+                        const Clipboard::FormatType& format);
 
  protected:
   // Converts |text| to UTF-8 and adds it to the clipboard.  If it's a URL, we