Add glue for supporting custom MIME types in DataTransfer.

content/renderer/renderer_clipboard_client.cc

Index: content/renderer/renderer_clipboard_client.cc
diff --git a/content/renderer/renderer_clipboard_client.cc b/content/renderer/renderer_clipboard_client.cc
index d87d527dcebf8e1d9675b6793da2aa9089894a34..87e8b60e3bf32f7a0a8ce4116dcbb455887c7c83 100644
--- a/content/renderer/renderer_clipboard_client.cc
+++ b/content/renderer/renderer_clipboard_client.cc
@@ -169,6 +169,13 @@ void RendererClipboardClient::ReadImage(ui::Clipboard::Buffer buffer,
   }
 }
 
+void RendererClipboardClient::ReadCustomData(ui::Clipboard::Buffer buffer,
+                                             const string16& type,
+                                             string16* data) {
+  RenderThreadImpl::current()->Send(
+      new ClipboardHostMsg_ReadCustomData(buffer, type, data));
+}
+
 webkit_glue::ClipboardClient::WriteContext*
 RendererClipboardClient::CreateWriteContext() {
   return new RendererClipboardWriteContext;