Add glue for supporting custom MIME types in DataTransfer.

ui/base/clipboard/clipboard_mac.mm

 // 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"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/file_path.h"
 #include "base/logging.h"
@@ skipping 266 matching lines @@
         [NSGraphicsContext graphicsContextWithGraphicsPort:gc flipped:NO];
     [NSGraphicsContext setCurrentContext:cocoa_gc];
     [image drawInRect:NSMakeRect(0, 0, width, height)
              fromRect:NSZeroRect
             operation:NSCompositeCopy
              fraction:1.0];
   }
   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 {
   NSPasteboard* pb = GetPasteboard();
 
   if (title) {
     NSString* contents = [pb stringForType:kUTTypeURLName];
     UTF8ToUTF16([contents UTF8String],
                 [contents lengthOfBytesUsingEncoding:NSUTF8StringEncoding],
                 title);
   }
 
@@ skipping 77 matching lines @@
 Clipboard::FormatType Clipboard::GetBitmapFormatType() {
   return base::SysNSStringToUTF8(NSTIFFPboardType);
 }
 
 // static
 Clipboard::FormatType Clipboard::GetWebKitSmartPasteFormatType() {
   return base::SysNSStringToUTF8(kWebSmartPastePboardType);
 }
 
 }  // namespace ui