[Qt] editing/pasteboard/can-read-in-dragstart-event.html and /can-read-in-copy-and-cut-events.html are crashing
https://bugs.webkit.org/show_bug.cgi?id=113126

Reviewed by Jocelyn Turcotte.

Source/WebCore:

Make it possible to read from a writable Clipboard.

Test: editing/pasteboard/can-read-in-copy-and-cut-events.html

* platform/qt/ClipboardQt.cpp:
(WebCore::ClipboardQt::getData):
(WebCore::ClipboardQt::types):
(WebCore::ClipboardQt::files):
(WebCore::ClipboardQt::readClipboardData):
(WebCore::ClipboardQt::hasData):
(WebCore::ClipboardQt::items):
* platform/qt/ClipboardQt.h:
(ClipboardQt):

LayoutTests:

Unskip now working editing/pasteboard/can-read-in-copy-and-cut-events.html.
The other test still needs better drag-and-drop support in DRT.

* platform/qt/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146910 268f45cc-cd09-0410-ab3c-d52691b4dbfc