Data Transfer Items File Dragout

BUG ID: 76367 Bugzilla bug Add DataTransferItems support for drag-and-drop'ed files and texts

STEPS TO TEST:

1. Open the $(WebKitRoot)/ManualTests/resources folder in your native file browser.
2. Drag and drop a file into the 'Drop files here' area below.
3. Drag out this link out of the browser window into a different folder in the native file browser).

Drop files here

TEST PASS: The same file you dropped in the step 2 should be dragged out to the folder in the step 3. The file should have the same content and the same file name as the dropped file. (NOTE: this does not work for multiple files yet.)

TEST FAIL: Nothing happens or a different file from the dropped one (likely a text file with the page title) is dragged out.