https://bugs.webkit.org/show_bug.cgi?id=117683

Reviewed by Brent Fulgham.

* dom/Clipboard.h: Removed declareAndWriteDragImage.

* page/DragController.cpp:
(WebCore::selectImageBeforeDragging): Half of the old prepareClipboardForImageDrag
is now refactored into this function.
(WebCore::DragController::startDrag): Where we called prepareClipboardForImageDrag,
instead call selectImageBeforeDragging and declareAndWriteDragImage. This is needed
because declareAndWriteDragImage needs to be a member function, for Mac at least.

* page/DragController.h: Added declareAndWriteDragImage.

* page/efl/DragControllerEfl.cpp:
(WebCore::DragController::declareAndWriteDragImage): Added empty placeholder.
It would be better to delete this file rather than having these placeholders.
I don't think EFL actually has drag support, and it makes work to have to keep
source files up to date that are really unused.

* page/gtk/DragControllerGtk.cpp:
(WebCore::DragController::declareAndWriteDragImage): Added. Calls Pasteboard::writeImage.
* page/mac/DragControllerMac.mm:
(WebCore::DragController::declareAndWriteDragImage): Added. Calls to DragClient, which
does the work.
* page/qt/DragControllerQt.cpp:
(WebCore::DragController::declareAndWriteDragImage): Added. Calls Pasteboard::writeImage.
* page/win/DragControllerWin.cpp:
(WebCore::DragController::declareAndWriteDragImage): Added. Uses Pasteboard functions to
do the work.

* platform/Clipboard.h: Changed the pasteboard function to return a non-const reference.
For now, it's not clear what const will mean for pasteboards, and it's currently not
possible to write to a const pasteboard, which we need to do in the new
DragController::declareAndWriteDragImage functions.

* platform/Pasteboard.h: Added a new writeMarkup function, implemented only for Windows
at this time.

* platform/efl/ClipboardEfl.cpp: Deleted declareAndWriteDragImage.
* platform/gtk/ClipboardGtk.cpp: Ditto.
* platform/ios/ClipboardIOS.h: Ditto.
* platform/ios/ClipboardIOS.mm: Ditto.
* platform/mac/ClipboardMac.mm: Ditto.
* platform/qt/ClipboardQt.cpp: Ditto.
* platform/win/ClipboardWin.cpp: Ditto.

* platform/win/PasteboardWin.cpp:
(WebCore::Pasteboard::writePlainTextToDataObject): Took out a pointless line of code.
(WebCore::Pasteboard::writeMarkup): Added. Currently implemented only for Windows.
This factors out a significant piece of DragController::declareAndWriteDragImage,
and will probably be handy for other platforms later.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153978 268f45cc-cd09-0410-ab3c-d52691b4dbfc