setData() of DataTransfer has a void return type
https://bugs.webkit.org/show_bug.cgi?id=133108

Reviewed by Alexey Proskuryakov.

Source/WebCore:
According to HTML5 spec, setData() of DataTranfer interface does not return value.
http://www.w3.org/TR/html/editing.html#the-datatransfer-interface

Test: editing/pasteboard/set_data_typeof_return.html

* dom/DataTransfer.cpp:
(WebCore::DataTransfer::setData):
* dom/DataTransfer.h:
* dom/DataTransfer.idl:
* platform/Pasteboard.h:
* platform/efl/PasteboardEfl.cpp:
(WebCore::Pasteboard::writeString):
* platform/gtk/PasteboardGtk.cpp:
(WebCore::Pasteboard::writeString):
* platform/ios/PasteboardIOS.mm:
(WebCore::Pasteboard::writeString):
* platform/mac/PasteboardMac.mm:
(WebCore::Pasteboard::writeString):
* platform/win/PasteboardWin.cpp:
(WebCore::Pasteboard::writeString):

LayoutTests:
* editing/pasteboard/set_data_typeof_return-expected.txt: Added.
* editing/pasteboard/set_data_typeof_return.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169327 268f45cc-cd09-0410-ab3c-d52691b4dbfc