Add glue for supporting custom MIME types in DataTransfer.

ui/base/clipboard/clipboard_win.cc

Index: ui/base/clipboard/clipboard_win.cc
diff --git a/ui/base/clipboard/clipboard_win.cc b/ui/base/clipboard/clipboard_win.cc
index 492dd31e6fb812de29c803aa58e411f933ebb28a..5c819c8a76b1363354dbd71bb5cfa834b3037b9b 100644
--- a/ui/base/clipboard/clipboard_win.cc
+++ b/ui/base/clipboard/clipboard_win.cc
@@ -544,6 +544,13 @@ SkBitmap Clipboard::ReadImage(Buffer buffer) const {
   return canvas.ExtractBitmap();
 }
 
+void Clipboard::ReadCustomData(Buffer buffer,
+                               const string16& type,
+                               string16* result) const {
+  // TODO(dcheng): Implement this.
+  NOTIMPLEMENTED();
+}
+
 void Clipboard::ReadBookmark(string16* title, std::string* url) const {
   if (title)
     title->clear();