Add glue for supporting custom MIME types in DataTransfer.

ui/base/clipboard/clipboard_gtk.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/base/clipboard/clipboard.h"
 
 #include <gtk/gtk.h>
 #include <X11/extensions/Xfixes.h>
 #include <X11/Xatom.h>
 #include <map>
@@ skipping 470 matching lines @@
                          false);
   {
     skia::ScopedPlatformPaint scoped_platform_paint(canvas.sk_canvas());
     cairo_t* context = scoped_platform_paint.GetPlatformSurface();
     gdk_cairo_set_source_pixbuf(context, pixbuf.get(), 0.0, 0.0);
     cairo_paint(context);
   }
   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 {
   // TODO(estade): implement this.
   NOTIMPLEMENTED();
 }
 
 void Clipboard::ReadData(const std::string& format, std::string* result) {
   GtkSelectionData* data =
       gtk_clipboard_wait_for_contents(clipboard_, StringToGdkAtom(format));
   if (!data)
     return;
@@ skipping 46 matching lines @@
       return clipboard_;
     case BUFFER_SELECTION:
       return primary_selection_;
     default:
       NOTREACHED();
       return NULL;
   }
 }
 
 }  // namespace ui